Tech Tree

Just a few more turns until the Giant Death Robot.

A staple of almost every strategy game is the ability for you to unlock new abilities for your units, or new unit classes entirely, by spending time and resources on scientific research instead of just bashing your opponent into submission with your existing ones.

Exactly how the tech tree works varies greatly depending on the game genre.

In Real-Time Strategy games, research is usually represented by specialized units or structures, with the pace of new tech development decided by how many of these the player has on the field. Research units often have weak attacking abilities (if they can attack at all) and must be protected from harm. Smart players and AIs will, of course, constantly be after these units.

New technologies typically allow for better armor to take more damage before dying, faster ground speeds, weapons that do more damage per hit, and increased sight and accuracy bonuses.

Tech upgrades are usually dressed to look genre-appropriate for the game. Researching advanced radar tech for your helicopters in one game will be instantly recognizable as granting your Paladins "Holy Sight" in another (or, in some cases, the same game).

Another key feature is that they usually follow a set order in which they must be researched. To give your troops armor-piercing shell upgrades, you may have to first research the advanced artillery tech, which in turn can't be done until you've finished researching basic cannon tech, etc...

Some games allow players greater influence over their gaming economies, and they can pour extra money into certain research projects to get them done faster while completing less urgent ones at their leisure.

Other times the development speed is static, and all that's required is that the player have enough gold, tiberium, wood, mana or whatever is needed to pay the upgrade costs for that tech.

The use of tech trees in 4X games is quite different. Tech trees typically do not have an on-map representation. They are a function of the empire itself. In such games, each empire's cities (or equivalent) provides some portion of research that is pooled until the civilization researches a particular technology. The rewards for a tech are improvements for "cities", new units or unit equipments, bonuses for a civilization researching them, or other such things.

Some Role Playing Games have the similar "Feat Tree", where at character creation time and at every N^th level up the player gets to choose new traits and abilities (feats) for their character, with some feats requiring other feats to unlock. Refer to Skill Scores and Perks for more information.

Tech trees are one of the big points where historians pick at games. It's a hierarchical view of science, research, and history. When compared with actual history, tech trees are wrong. On the other hand, the few attempts at doing something different have wound up pulled from any final version, with good reason.

Either way, researched technologies in many games, most often Real-Time Strategy, have an annoying habit of disappearing once the current level/mission is completed, forcing you to spend time researching them all again in the very next round.

See also You Have Researched Breathing, Reinventing the Wheel. A Tech Tree may be prone to Interface Spoilers, or conversely, it may become a Guide Dang It! to make an informed decision.

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Examples

First Person Shooter

• Call of Duty: Modern Warfare II treats its weapons and their associated attachments much more in line with this, compared to earlier games where weapons are unlocked in a specific order and attachments need to be unlocked for use with every individual weapon. Weapons are arranged by weapon platform, where weapons that share a basis in reality are unlocked by leveling up earlier weapons in that platform, e.g. leveling the starting M4 gradually unlocks the FTac Recon battle rifle, the FSS Hurricane submachine gun, and the 556 Icarus light machine gun, the latter of which unlocks the burst-firing M16. Attachments for the most part are also treated as universal, whether within their specific weapon platforms (barrels, magazines, stocks and rear grips) or across all weapons (optics, underbarrels and lasers), with some other distinctions within those (muzzle attachments based on caliber, grenade launchers unlocked with one weapon family can be used with one or two others, the highest-magnification optics exclusive to sniper rifles, etc.), meaning once you've unlocked an attachment by leveling its constituent weapon (e.g. the FSS Covert IV suppressor from getting the BAS-P submachine gun to level 3), it can be attached to any compatible weapon so long as it's leveled enough to open up the slot the attachment in question goes in.
• In E.Y.E: Divine Cybermancy, enemies will sometimes drop research briefcases upon dying, which can be collected to unlock new avenues and items for research (to unlock new weapons, abilities, and stat bonuses). Some items require multiple other objects to be researched, such as the Distortion Hammer first requiring the Distortion Inductor and Lost Technology to be researched (both of which also have other research prerequisites). Players select an item for research in their character menu, and then selects how many scientists to use - more scientists will research faster, but greatly increases the cost of research.

Four X

• Age of Wonders 4 has adds a non-linear element to the tech tree. As the player is a Sorcerous Overlord, research is divided into numerous Tomes which each contain 5 to 6 research topics organized around a particular theme. Items within a tome can be researched in any order, and there is an opportunity to unlock a new tome every few research cycles. Tomes are divided into tiers and while unlocking one of a higher tier requires researching two of the tier below, there is no specification as to which two. A ruler can therefore go from starting out with Nature tomes at tier 1 and study Chaos and Astral magics at tier 2. Only the highest-tier tomes require a certain amount of affinity with the associated magics to unlock.
• Ascendancy has a three-dimensional tech tree that is simply stunning in its scope and variety. Unlike many games, it is not necessary (or even possible) for a player to acquire all technologies to win — the tree branches in many wildly different and interesting directions, allowing races to specialize in something strange and unusual yet still have a strategically versatile "power set".
• Galactic Civilizations II has a large but fairly simple tech tree; all technologies have a single prerequisite^* Although some require you to be of a specific moral alignment to unlock them. A long, time-intensive branch dealing with philosophy and the nature of existence has no mechanical in-game benefits, but researching the final step of this branch triggers the research victory condition: the entire population of the player's race transcends into Energy Beings.
  • The branch in question consists of five increasingly expensive (in terms of research points) parts, to wit: "Deeper Knowledge," "Galactic Understanding," "Near Omniscience," "Beyond Mortality," and, finally, "Technology Victory." The Torians have a similar branch that does reward +5% research for each step along the way, to make up for their limited tech buildings.
  • As of the Twilight of the Arnor expansion, there's a whole orchard of tech trees, for each of the different major races, emphasizing their different strengths and weaknesses and going deeper into the history and character of each race.
• Civilization, as the name implies, has an absurd Tech Tree that spans all of human history from the stone age to the space age and beyond. One of the final Wonders of Civilization grants instant victory upon completion of mankind's first interstellar spaceship, which leads to:
  • Sid Meier's Alpha Centauri also has a really complex tech tree, like most Firaxis games, where the player must research all sorts of future technology until he can reach the Threshold of Transcendence. Once the player finishes the Ascent to Transcendence project, the player's civilization will Ascend to a Higher Plane of Existence.
    • An interesting twist is the ability to make tech developments random as you progress. You still have to research everything in order but rather than selecting individual nodes to research, the player selects a general direction they want to research in (along the four disciplines the game offers: Conquer, Discover, Build, Explore) and nodes are selected at random between nodes matching the disciplines chosen. It's a way to add significant Replay Value to the game.
  • Definitely in Civilization 2 (and probably in the original Civilization) the cost of getting new technologies depends on the number of technologies you already have - so getting even one technology that you don't need is extremely expensive. As a result good players had absurd technology trees. Freeciv fixes this problem by making the cost of technology depend only on its position in the tree.
    • The disowned spinoff Call to Power II gave each technology a fixed amount of research you had to accumulate to research it.
  • Civilization Revolutions has a much shorter tech tree (48 techs). It is occasionally possible to research a higher technology without all of the prerequisites.
    • But Civilization 4, the game that Revolutions is most closely related to, has a larger tech tree; Revolutions is in some ways a stripped-down version of Civ 4. (The spaceship win condition includes reaching the planet.)
  • In Civilization V, in order to research any technology that has multiple prerequisites, all prerequisite techs - not one, not some, but all - must be researched first. On the one hand, it makes for somewhat more realistic tech progression. On the other hand, this makes it impossible to skip over unneeded technologies.
    • In the short-term one can "beeline" one branch of technology without touching other parts, though a balanced civ will find most techs tempting in one way or another. This results in some odd combinations, like being able to make a chariot archer without archery, or the giant death robot without robotics, or even archaeology without mining.
    • Civ IV was the only game in the series that had optional prerequisites, where you could choose one of a pair of technologies to get to the next one (leading to such potential oddities as a society discovering fusion without ever learning agriculture), though only Civ III railroaded you to quite this extent. That game had you research the majority of the technologies in any given age before you could research any technologies in the next age.
  • Civilization VI has two tech trees: one for science and one for government and culture. Progress through each tree is largely independent of progress through the other. A later update added a "shuffle tech tree" option in which the structure of the tree is randomized within each era and which tech leads to what is hidden until either its prerequisites are researched or its associated eureka/inspiration is gained (actions that happen on the map that would logically spur its development, like finding a natural wonder jump-starting Astrology); it's meant to prevent Complacent Gaming Syndrome by players falling into a set tech tree researching order, though it can lead to some rather weird things like needing Sailing in order to research Iron Working.
  • In the board game Civilization that loosely inspired the computer game, each technology gives a discount to the price of acquiring certain others. It is prohibitively expensive to research the most advanced techs until you have the earlier ones that give discounts. Some techs are more useful for the discounts they provide than for their own effects.
• The base Space Empires games already have sizable tech trees that grow larger with every iteration of the game. They are also quite moddable, and modders have created veritable jungles of tech trees s a result.
• Sword of the Stars has a large interconnected tech tree. With the added factor of each race getting various percentage chances to have the various technologies in their tree, meaning that no two games, or players, are completely identical tech wise.
• The Master of Orion series uses slightly different tech trees in each game:
  • In the original game, each empire had a percentage chance of each tech being available for research, the odds determined by their race's affinities. These techs were divided into six parallel teach 'ladders' that could be researched simultaneously.
  • In the second game, each tree has multiple tech choices at each level. Most races can only receive one tech per level through research, and races with the "Uncreative" trait cannot choose which one they get. Creative races get everything for the same price a regular race pays for one item.
  • In the newest game, the tech tree is the same for all races, but some research gives you two or three options, of which you can only choose one. For example, researching Genetic Mutations always gives you Terraforming, and you have a choice of Telepathic Training (improves your spies) or Heightened Intelligence (improves your scientists). Races that are Creative will get both. Races that are Uncreative don't get to choose; the game picks the option at random.
• Players in Star Ruler start out with a selection of basic technologies (such as economics, particle physics, and ballistic weapons). To unlock new research avenues, players select "hunches" and "guesses" on unlocked research items, which will lead to a random adjacent research item inside the hexagonal research grid. Metallurgy, for example, has ties to chemistry and nanotechnology. Once a research avenue is unlocked, unlocks are researched linearly; researching lasers will first unlock standard lasers, then pulse lasers, and so on. Because technology improves constantly with every level invested into a research avenue, it's critical to constantly expand your scientific laboratories, otherwise you'll be left behind while other players are building starships the size of planets, ships that can carry bigger ships inside themselves, and killing stars.
• Stellaris has an interesting tech tree in that there's a strong random component. Techs are divided into three categories: Physics, which governs things like laser weapons for spaceships or power plants for your Energy Economy, Society, which helps you Terraform worlds or better manage your star empire, and Engineering, which unlocks new classes of ships and better factories to help you produce them. Completing techs unlocks better developments in those lines, so researching mass drivers will lead to coilguns and eventually railguns, but instead of having the full tech tree available to choose from, you're instead "dealt" several research options (three as standard, which can be increased in various ways) from a "deck" of available techs in each of those three categories. The draw chances for a given technology can be manipulated based on what you've done or how you've defined your empire. For instance, an empire with Militarist ethics is more likely to pull the technology for more advanced starships, whereas an empire that has invested the resources into building multiple Starholds will give you better chances of drawing the technology for the next step up, Star Fortresses. Advanced players can "plot a course" for drawing specific powerful techs as early as possible by manipulating draw rates in their favor and avoiding technologies that open up more unrelated techs which would thus dilute the pool. Fortunately, technology for starship components can be unlocked and accelerated by having a science vessel scan post-battle wreckage, allowing you to reverse-engineer better components by surviving encounters with a more-advanced opponent - such techs will always be available in addition to your standard "hand" of research options until you finish them.
• The Rebuild series of games has a simple tech tree that's generally divided into three disciplines: zombie combat, infrastructure, and social. Except for the zombie bits, the tree is deliberately framed as Reinventing the Wheel, given the After the End setting.
• Humankind has a normal tech tree for this sort of game that opens new units, buildings, and etc.

Hack And Slash

• This can also be seen in Diablo 2. Sometimes this makes sense, like how a Sorceress has to learn the basic Ice Bolt spell before learning the more advanced Blizzard. Other times, like how the Barbarian has to learn Leap (what it sounds like) before Whirlwind (a spinning blade attack), it's obvious they're just prerequisites for prerequisites' sake.

Idle Game

• Cell to Singularity: Evolution Never Ends: The initial display of all your life and upgrades is done with branches and nodes, with new forms of life often being locked before getting necessary upgrades, with the game calling it "Tech Tree of Life". There are several other tech trees unlocked later.

MMORPGs

• Each World of Warcraft class has its own, specialized tech tree, with abilities that can only be gained by putting points into it. One point is gained every 15 levels—you pick one of three, and cannot backtrack to pick up a second one from a lower tier.
• This trope is a huge point of the MMORPG A Tale In The Desert, where practically the entire playerbase rushes to unlock technologies as soon as they're available, no matter how useful they turn out to be in the end.
• EVE Online has tech trees as well. In order to fly certain ships or use specific modules, you need to research a multitude of skills, some of which take weeks to learn.
• World of Tanks uses the Tech Tree as a form of Experience level AND tech tree. As you fight battles you earn XP and credits, which you use to upgrade your existing vehicle, and then purchase the next higher tier vehicle or vehicles in line.

Real Time Strategy

• In 0 A.D., certain requirements must be met before you can upgrade you town and build more advanced structures.
• Age of Empires III has an interesting take on this trope. While it features a relatively mundane tech tree for most of its buildings and units, players can customise available shipments from their Home City by setting up a virtual "deck". This means that two players' play styles can vary dramatically even if they use the same nation, depending on what types of shipments they choose to make available.
• Haegemonia: Legions of Iron had a research system that needed to be managed along with the players units. Since the multiplayer mode made it so that players on the same team were commanders of the same fleet, players could split the duties by having one team member manage colonies and research while others managed combat.
• Warzone 2100 is absolutely crazy about this, since it has several hundred techs, probably range up to thousands, to be researched. Good thing it averts Reinventing the Wheel.
• Paradox Interactive has tech trees that tends to be rather complex.
  • Europa Universalis has tech "levels" based on four different categories (Land, Naval, production and trade techs) and a fifth category, "stability" that isn't tech per se but gets money from the same budget. EU3 adds a fifth tech category ("government") tech is researched simply by spending money from your budget, but the tech cost is modified by... Well, a shitload of different factors. Different levels unlock different types of upgrades and buildings.
  • Hearts of Iron 2, set during World War II, has a more conventional tech tree, with advances leading to further advances in various categories. All of them have a "historical year" which make them much more expensive to research before their time. Research is carried out by country-specific "Tech Teams" such as Boeing or Wernher von Braun. Of particular note is the "Secret" category, which consists of tiny groups of unrelated advances - electronic computers, nuclear fission, rocket interceptors - that become available a short while after their prerequisites from other categories are reached.
    • By contrast, Hearts of Iron (the previous game in that type) has a vastly more complicated tech tree with at least several hundred techs. Moreover, you research the technology using the same industrial capacity you use to build units, which creates conflicts of interest.
    • Hearts Of Iron IV features no less than 12 broad categories of research - infantry, tanks, artillery, support companies, ships, aircraft, industry, science/engineering, and doctrines for land, sea and air - all of which must be researched using a limited number of research slots, of which countries may start with as few as 2 or 3, and will never have more than 5 or 6. Additionally, certain technologies have prerequisites in other categories - researching signal companies, for example, requires both motorization and radio tech to have already been researched - and the penalties for researching tech ahead of their historical year are carried over from previous games. The game also has a separate "National Focus" tree. Each National Focus researched grants one of any number of wide ranging perks, but many require not only one or more prior Focus to be completed - sometimes from different branches of the tree - but may also require certain game conditions to be in effect, or even the cooperation of another country in order to complete.
  • Victoria: An Empire Under The Sun has a relatively simple tech tree with different "levels" of technology, but each technology "level" will, at certain randomized intervals, trigger "inventions" which provide most of the benefits. Research is based primary on your country's literacy rating but also on the makeup of your society (clergy and clerks providing the most research output, although the "darwinism" invention crashes clergy's research output and doubles that of clerks)
  • Crusader Kings is set in medieval times and uses a "directed fluke" system: you pick techs and discover them in your capital a random number of years later. However, all technologies are features of particular territories, not their owners. Paris will not stop having an university because it's inherited by a monarch whose home doesn't, nor will Finland revolutionized its agriculture just by falling into the hands of a country that has. Techs spread over borders and trade routes, affected by politics and infrastructure.
• StarCraft requires specific buildings to produce units and research upgrades, and most buildings have other buildings as prerequisites for construction. The structure of the building hierarchy varies for each of the three races, with zerg having a tier based system, protoss having 3 largely independent tech paths, and Terran having a shorter central path with several large 'branches' for better units in certain classes. Upgrades offer either a unit-specific ability or improvement (such as increased attack range for the zerg hydralisk or a short range teleport for protoss stalkers) or a generic attack/defense boost for a class of units (e.g. increased attack power for all air units). Upgrades cost a fixed amount of resources and take a fixed amount of time to research once purchased.
• One of the daddies of them all was Utopia, back in 1991, although it may have been pre-empted by Reach for the Stars, released eight years earlier. Utopia was followed up by K240 in which the 'research' is already done, it just has to be purchased (but making money requires selling your precious ores which you may want to use to build starships).
• Command & Conquer: Red Alert 3 is odd about this, all sides have to build a tech building to get the most advances stuff but Allies and Imperial have to pay for further upgrades, either in the form of security clearance for the construction yard (allies) or upgrades for individual buildings (imperial), the soviets just need a tech building.
  • This is actually a balance mechanic, meaning that Soviets (who also have the ability to build secondary construction units and a simple build system) have the fastest tech rush, and often dominate the early game, whereas the Allies (who need to stop construction to go up a tech level and have the slowest, if safest building system) are given borderline Game-Breaker units to compensate.
• The Total War series used a tech-tree without actual research. Better versions of existing buildings become available when a city grows to a certain size, and in turn allow recruiting better units. Therefore, reaching the top tier of production usually involved protecting your kingdom long enough to let its cities grow big.
  • In Empire: Total War, a more conventional tech tree was introduced - you could study new ideas in three separate trees (social, economic, military), which in turn unlocked new buildings, units, strategic advantages, and even new actions to perform during battles. Unfortunately, the designers went too heavy on the Acceptable Breaks from Reality, allowing players to research things like ocean-going steam ships and rifling in the early 18th century. It didn't help that many players (and not just the veteran fans of the series) found the game to be sub-par in several other respects.
    • The expansion/sequel Napoleon: Total War used a tech-tree as well, and in a case of subtle Retcon featured a Tech Tree very similar to that of its predecessor (that is, containing many of the same techs), except now it was the 19th century and thus more suitable... except many of the technologies on the tree were still from way beyond of Napoleon's time and the game's scope.
• Achron has an interesting spin on this. Each faction has a very small, very flat tech tree (usually amounting to around six upgrades or so) and they are explained away as "improving infrastructure" (as opposed to "research"). The interesting bit is the way this interacts with the time travel mechanics: It's possible to arm your units with weaponry from the future, or reinforce your army with units you can't technically build yet.
• 8Realms has researchable tech trees available via the Library or University.
• Jeff Wayne's War of the Worlds has a mostly hierarchical tech tree, though some things are instead unlocked as counters, AA Guns after encountering flying machines for example.
• Kingdoms Reborn: Citizens constantly generate science points. These can be used to unlock items on the Tech Tree (which mostly contains buildings) and Upgrades Tree (Exactly What It Says on the Tin).
• Homeworld has a relatively flat tech tree, with upgrades unlocked by research ships. Like most other things in the campaign, research is retained between missions. As a general rule, researching a class of ship would unlock a generalist basic version, then researching a weapon system would unlock the ship that uses it, but ships themselves had no upgrades - you could either build them or not. The "expandalone" Cataclysm introduced upgrades for ships, but each individual ship needed to power down to upgrade itself after the research was performed except strike craft; they have to come in to dock for refits. Homeworld 2 took it in a different direction, as the tech tree now not only included research but also added more base building in the form of mothership modules; capital ships included a fixed number of hardpoints for factory systems or specialized gear, and no one ship could unlock all of its abilities at once, the player had to pick and choose.
• Supreme Commander doesn't have one, or rather has a very flat one. A given unit or structure has a tech level that describes its complexity, and if you have a factory or engineer of the right tech level and environment type (sea, air, or land) you can build it. There is an upgrade hierarchy for the player's commander and secondary commander, but those are more "mutually-exclusive customization options to suit playstyle" than "new discoveries".
  • Supreme Commander 2 on the other hand does have research, although it functions more like an experience point skill tree system. Research points are accumulated by research structures (essentially big computer cores that analyze data and run simulations) and are also gained in combat (observing your units in action gives the boffins clues on how to improve them).
• Dawn of War: Most factions (except the Tau, Eldar and Dark Eldar) use a tier system by upgrading their HQ building.
  • The Tau are the only faction with Divergent Character Evolution: Either you pick the building that lets you build Hammerheads and Crisis suits (very powerful tank and jump suit) or the one that lets you build Krootox and Kroothounds (strong melee units), which also gives health upgrades to most units and increased sight range (it's believed by some that the life upgrade was supposed to go along with the first upgrade, either not corrected or deliberately left in).
• Machines: Wired For War: Both civilian and military units/building need to be researched. The military tree is split into 'energy' and 'kinetic' weapons, with the most power units towards the top. Extra special units require both paths to be researched. Info to built new structures/units can also be stolen rather than researched.
• Forged Battalion has a two-tiered tech tree. First is the standard battlefield tech three, where building a specific unit requires certain structures. Second is the faction tech three, which players unlock and which allows players to design new units for their faction.

Role Playing Game

• All of Arcanum's technology trees were single-pathed, non-cumulative skills that allowed you to craft something. All crafting trees had a single theme, some useful only at the intended level of reachability, some upgradeable at higher tiers, some upgradeable with cross-tree synergy, and some worthless for anything except to unlock higher tiers. But there were some trees that the top skill is the only reason to invest character points, and others where the top skill is found to be practically worthless; that is worthless under any circumstance that you could've imagined it being valuable for.
• Atelier Ryza 2: Lost Legends & the Secret Fairy introduces a Skill Tree. You earn SP through various methods, such as performing synthesis and completing sidequests, and can spend it to progress on the Skill Tree, which unlocks new alchemy recipes and other upgrades.
• Borderlands 2 has a three-way tech tree. Upon getting your basic ability, you then start getting a point for each level gained. You can then choose how to distribute the points to expand your capabilities.
• The Enchanted Cave, but only in the second game.
• Etrian Odyssey has always had the system of "some skills require leveling up other skills to learn them", but it wasn't until Etrian Odyssey IV: Legends of the Titan that the skill list started being displayed as a flowchart of skills rather than a one-column list to better show this trope.
• Legend of Mana starts you off with about eight basic moves (and no super moves); learning new moves involves you putting moves together, getting experience, and hoping the Random Number God is merciful.
• SaGa Frontier has an absolutely immense tech tree, with over 100 abilities that can be learned from each other with various degrees of success depending on what ability is being used. And that's not even including the various combination attacks that can be performed between party members.
• In Unleash the Light, each party member has two sets of skill trees that you can spend Skill Points on. Each tree branches out into two upgrade paths after the first one before merging into the final upgrade.
• Your Bizarre Adventure (a JoJo's Bizarre Adventure Fan Game): Upon leveling up, the player is given points that can be allocated in one of three different skill trees: one for the character's basic stats, one for their Stand, and one for their fighting style. The former consists entirely of upgrades, while the latter two alternate between upgrades to existing abilities and unlocking new ones. In any case, many of them must be unlocked in a specific order, though there are often separate branches for different upgrades. Stand skill trees are sometimes given thematically-appropriate shapes; Grey Rapier's^note a renamed Silver Chariot resembles the sword it uses in combat, for example.

Simulation Game

• Ace Combat:
  • Ace Combat 5: The Unsung War unlocks basic planes by completing missions, then allows you to unlock later variants and upgrades by flying and making kills with those basic planes.
  • Ace Combat Infinity expanded out with an Aircraft Tree, where after each sortie a little bit of research is performed on every plane, weapon, and upgrade currently available. Once research is completed on one of these, it can be properly purchased, which unlocks any further research nodes past that.
  • Ace Combat 7: Skies Unknown uses the same Aircraft Tree as Infinity, though without having to spend time researching unlocks. There's also a separate branch for high-end, multiplayer-only upgrades.
• Pretty-much the entire point of the open-source game Endgame: Singularity is to research the entire tech tree while not being discovered. Sounds easy, right? Well, not in the early stages of the game. Once you have Quantum Computers, however...
• Graveyard Keeper stars a tech tree for all of its upgrades, helping the titular character autopsy corpses and prepare them for burial more efficiently, branch into highly efficient farming, and harness dark energies from beyond the veil to help him improve the quality of his graveyard.
• The skill system in Growing Up is like this, with some skills following a singular learning path and others branching out after learning the first few. You can only pick one path for skill trees that branch out, like choosing to specialize in fiction over journalism in the Creative Writing skill tree.
• Honey, I Joined a Cult has you build a research room to be able to research upgrades for your cult. You develop new therapy rooms to fleece your followers, upgrades to your maximum caps of cultists and followers, better sermons or ways your leader can inspire the cult. There is also a second leader-only tech tree which directs the future of your cult: such as, as of early access, trying to make contact with dark, sinister beings.
• In Hundred Days, the Technologies section of the menu has four tech trees to buy upgrades for: Board Upgrade^note to increase the playing field and make more turns using cards, Tool Shed, Winery, and Warehouse^note to upgrade the marketing sector. The trees usually branch out into two paths, with a few merging into the final upgrade.
• The career mode in Kerbal Space Program has a Research tree. Doing scientific experiments, launching and retrieving spacecraft, and creating crew reports generates Science, which can be used to unlock new spaceship and rover parts in the research building.
• A Kingdom For Keflings has a blueprint tree - completing a building unlocks those below it. The tree occasionally branches, and it's often impossible to unlock multiple branches in one kingdom.
• In Let's Build a Zoo, you can unlock new decorations, facilities, enclosure types, and other items from a grid using research points, which are gained every few seconds as long as you have researchers. You can only unlock something if it's adjacent to something you've already unlocked.
• The Naval Ops series uses a set of Tech Trees to organize research. One tree for torpedoes, one for lasers, and so one. Figuring out just how to unlock certain pieces of equipment can be an exercise in Guide Dang It!.
• Parkasaurus has two currencies that can be used to unlock new items from two trees. Hearts buy items that are used in dinosaur exhibits, while science credits buy items that appeal to guests.
• Justified in-universe in Prison Architect as the "Bureaucracy" menu, where unlocking each element of the tech tree requires specialised staff members to spend time doing paperwork to legalise the usage of it within the player's prison.
• SimCity (2013) has one, based primarily around the City Hall. As population increases, slots open to upgrade the Hall with new Departments such as Finance, Transportation, Education, etc. in order to unlock special buildings related to that issue. The Hall has limited upgrade space, but it unlocks buildings for every city in the region. Some buildings have other prerequisites as well.
• Syndicate required you to research new weapons and upgrades before you could buy them for your team of cyborgs between missions. Which is fair enough (laser rifles and advanced bionic arms probably take a bit of working out), but it got a bit silly when your evil 21st century corporation could field a squad of bionic hitmen but you couldn't even build uzis for them until you'd done the research.
• In To the Rescue!, you earn Skill Points at the end of the day by successfully adopting out dogs, which you can spend on four different skill trees to unlock new skills in handling, logistics, public relations, and handiwork. You can also exchange your Reputation for Skill Points.
• A central mechanic of The Universim is the research menu. Whenever you click on a node, you'll have to wait for a few minutes as your Nuggets research it. Once it's done, you'll unlock perks such as new types of buildings or increases to the Nuggets' stats. You can queue up to five items at a time, and a few have additional prerequisites.
• Workers & Resources: Soviet Republic: Certain buildings (like advanced industry or airports) and game mechanics (such as the ability to accept foreign tourists, locate natural resources on the map and Secret Police), have to be unlocked by research in the Technical University, Medical University and Party Headquarters.

Turn Based Strategy

• The old turn-based strategy game Deadlock and its sequel have an elaborate tech tree that works just like that. It's also possible to buy technologies on the black market (how the dealers got hold of super-advanced technology is never really explained).
  • It's because you and the black market aliens all had the tech beforehand: the races that contested the planet all agreed that each colony had to start off at with limited resources and technology. You're not inventing the technology; you're developing the tools to make the technology.
• Heroes of Might and Magic has blueprint trees for each town type. In later games each town has a different path when it comes to horde production. To make towns more balanced, some of the towns with overall weaker units can build their higher level horde production buildings much earlier than towns with more powerful armies (ie the Stronghold in III being able to build the Behemoth structure in three days from scratch). IV forces the player to choose which 2nd, 3rd, or 4th level units they want from a town. V complicated the formula from III with town levels: a town has to have a certain number of buildings already built before it can build higher level buildings like a city hall or capitol. Hero development in IV and V has a tech tree of sorts with certain skills needed to unlock new ones (and a very specific path is needed to unlock a Hero's Ultimate Skill in V).
• Each race in Disciples 2: Dark Prophecy has a different blueprint tree for each type of unit (ranged, melee, magic, and support). Adding another layer of strategy, once you choose which path to take for certain unit types for certain races you can't build the other path. For example, the Empire's initial support unit, the Acolyte, can be upgraded into either a more powerful single healer unit or a weaker mass-healer, but once you pick one upgrade structure to build you can't build the other one.
• Advanced Strategic Command has a rather flexible tree, in that each technology may require either all or any prerequisites and may be blocked by others (the basic campaign gives choice of Light Turret vs. Mobile Air Defence variants). Tech Level listed separately, so the "soft" requirement check isn't applied to it. Elements are either abstract or has a Related Unit, in which case its sprite is present in the tech list.
• XCOM series and its spiritual successors have a lot of alien technology to capture, study, adapt and improve. Usually there's not a single big tree, but many small ones started by a single artifact or a group of artifacts.
  • The original X-COM: UFO Defense (UFO: Enemy Unknown) was probably the simplest in that regard. Most artefacts can be studied immediately; studying plasma rifle and its clip allows to invent a craft plasma cannon; same for blaster launcher and its bomb; studying pieces of crashed UFOs allows to invent your own anti-gravity craft; interrogating a telepath unlocks psionics; capturing and interrogating aliens unlocks alien strategy studies — and you are always told whom to interrogate to advance further. Some interrogations gave inconsequential pieces on information like UFO names or something useful like hyperwave decoder. Then there were several purely Earth inventions that didn't need unlocking, including the laser weaponry line.
  • XCOM Terror From The Deep made things more interesting, with more artefact research unlocked by researching weaker or entirely unrelated artefacts. With several cases of Guide Dang It!. Vibroblade and thermic lance can only be studied if you have respectively Calcinite or Gill Man corpses in storage on the same base. Lobsterman commander unlocks researching T'leth and Leviathan, while Tasoth commander unlocks only T'leth, but prevents unlocking Leviathan — you can learn the location of The Very Definitely Final Dungeon, but can't develop a ship to reach it.
  • XCOM Apocalypse and XCOM Interceptor continued the idea with multiple research lines converging to an ultimate technology.
  • UFO After Blank had research trees along the same lines. The game plot greatly depends on that.
  • The reboot, XCOM: Enemy Unknown, spices things up by giving your bonuses to researching certain technologies if you can successfully capture and interrogate certain aliens - nabbing a Sectoid Commander will help you research Psionics faster, bringing back a Muton will help you develop plasma weapons, and so on.
  • XCOM 2's War of the Chosen expansion combats the tendency for players to go through the tech tree in a certain order by having your head scientist randomly feel "inspired" to finish one technology option much faster than usual, but only if you start working on that technology immediately. This can let players get certain equipment or facilities unlocked weeks or months earlier than expected, and can persuade them to try new paths through the game's tech tree. War of the Chosen also adds "breakthrough" researches which also must be researched immediately and offer a permanent boost such as increased damage for a certain weapon class/tier or reduced cost for a facility, leaving the player to choose if the strategic bonus is worth delaying their other research.
  • Mods based on OpenXcom, such as Piratez and The XCOM Files tend to make their research trees large and with many interconnections. Sometimes invoking Gotta Catch Them All (an invention is unlocked by researching 1-2 dozen artifacts) or You Have Researched Breathing (justified by After the End and Obstructive Bureaucrats respectively).

Non-video game examples:

Anime and Manga

• Dr. STONE displays tech trees for Senku's long term goals, documenting the process from raw material to finished project. His previous inventions often come up as a component in making new ones. However, it is evident that he has not ever tried a single real example.

Tabletop Games

• GURPS has a sort of "magic" tree. In order to learn advanced spells you have to learn simpler spells that presumably give the character the knowledge needed to understand the more complicated ones.
• Magic: The Gathering has the "Level up" mechanic from the Rise of the Eldrazi expansion, which allows you to sink additional mana into the creatures you already have to upgrade them to stronger versions.
• Starfire introduced Tech Trees starting in 4th Edition, replacing their old system of Technology Levels.
• Dungeons & Dragons 3.X had the Feat Tree example, and actually used those words to describe it. Feats were granted at level 1, level 3, and every 3 levels thereafter^note As developers have pointed out, it is a straight progression if you assume that you get the first feat at a theoretical 'apprentice' level 0 and it just is noted at level 1 because you can't really adventure as a level 0 character. Pathfinder has a feat at every 2 levels, as it assumed you actually get the first feat at level 1.. Many Feats required other Feats, and there were even some deliberately weak Feats (for example, Endurance gave a +4 bonus to saves to resist exhaustion and the ability to sleep in Medium armor, which would be relevant only if the GM was a whole-hearted Rules Lawyer) that were primarily used as prerequisites for above-average Feats to keep them balanced (Endurance was a prerequisite for such Feats as Diehard (lower penalties for being below 0 hit points and takes more damage to kill you) and Steadfast Determination (use the CON score you were prioritizing for both Fortitude and Will Saves, making the WIS score you were using as a Dump Stat directly govern nothing)). Being able to climb a Feat Tree was pretty much all the Fighter class had going for it, as its only class feature was a bonus Feat (taken from a very long list) at first level and every even level. As such, there were several Feat Trees created exclusively for Fighters, even requiring a minimum Fighter class level to take.
  • The alternate magic system in Drop Dead Studios' Spheres of Power for Pathfinder works like this. This is done to help make more thematic characters and to avoid Linear Warriors, Quadratic Wizards.
• Older games using the FATE system, such as Spirit of the Century, tend to effectively have "stunt trees"; some stunts (basically the system's feat equivalent) have specific others as prerequisites or require a number of other stunts from a given category before they can be taken. For example, Lair requires Headquarters, of which it is basically a "luxury version" with more options, while Developed Immunities, which makes the character highly resistant to poison, requires at least one other Endurance stunt to be taken before it (Endurance itself is a skill in the game as the system doesn't distinguish between those and classic "attributes"). As the latter case illustrates — Developed Immunities could e.g. go together with Last Leg, which allows the character to spend fate points to hang in a fight just a bit longer but doesn't really have much if anything to do with acquiring poison resistance —, the actual connection between prerequisite(s) and "higher-level" stunts can be a bit shaky at times.
  • The Fate Core System and its "quick-start" version Fate Accelerated Edition released in 2013 on the other hand subvert this trope by making stunts explicitly more freeform. (While it has always been true that a group could create its own stunts, previous implementations were often long on "stock" stunt shopping lists and short on actual guidelines how to do so.) It's still possible to create stunt "trees" if desired using these rules as well, but those are now more simply another option for the GM's and players' creative toolbox and less something hardcoded into the rules themselves as presented.
• Feng Shui's fu power system works this way, in contrast to the other major schticks that the game has to offer. The Path of the Healthy Tiger, for instance, allows one to specialize in either healing and pressure point attacks, or vicious counterattacks, but the ultimate power of the Tiger style, Storm of the Tiger, requires mastery of both paths.
• Twilight Imperium has a fairly large tech tree, represented by a deck of cards for each player. The expansions add unique racial technologies for players as well. On most game rounds each player will probably get a chance to gain one or two technologies - however, since a typical game only lasts about 10 rounds and there are about 30 technologies in the tree, it's effectively impossible to get every technology. Usually a player will aim for a specific technology at the end of one branch, or 2-3 technologies in the middle of the tree (based on the current objectives, races in the game, etc.)
• Stellar Conquest (Metagaming, 1975) has three tech trees (ship speed, weapons, technological research), although each tree has only 3 levels and 6 technologies.

Real Life

• Many school and university courses give students a large degree of freedom in choosing modules or papers, but many modules require students to have previously studied certain other modules. Requirements can often become complex enough that progression through the whole course resembles a video game tech tree: see, for instance, this diagram illustrating module dependencies in Oxford's undergraduate Mathematics course.

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