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 RealTimeStrategy 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 FourX 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 Game}}s have the similar "Feat Tree", where at character creation time and at every N[[superscript:th]] LevelUp the player gets to choose new traits and abilities (feats) for their character, with some feats requiring other feats to unlock. Refer to SkillScoresAndPerks 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, [[YouFailHistoryForever tech trees are wrong]]. On the other hand, the few attempts at doing something [[VideoGame/MasterOfOrion different]] have wound up pulled from any final version, [[AnachronismStew with]] [[AcceptableBreakFromReality good]] [[GameBreaker reason]].

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

See also YouHaveResearchedBreathing, ReinventingTheWheel. A Tech Tree may be prone to {{Interface Spoiler}}s, or conversely, it may become a GuideDangIt to make an informed decision.
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!!Examples

[[foldercontrol]]

[[folder: First Person Shooter ]]

* In ''Videogame/EYEDivineCybermancy'', 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 [[RPGElements stat bonuses]]). Some items require multiple other objects to be researched, such as the [[DropTheHammer Distortion Hammer]] first requiring the Distortion Inductor and LostTechnology 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.

[[/folder]]

[[folder: Four X ]]

* ''VideoGame/{{Ascendancy}}'' has a three-dimensional TechTree 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".
* ''VideoGame/GalacticCivilizations II'' has a large but fairly simple tech tree; all technologies have a single prerequisite[[labelnote:*]] Although some require you to be of a specific moral alignment to unlock them[[/labelnote]]. 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 [[AscendToAHigherPlaneOfExistence transcends]] into EnergyBeings.
** 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.
* ''VideoGame/{{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:
** ''SidMeiersAlphaCentauri'' 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 AscendToAHigherPlaneOfExistence.
** 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. [[MisaimedRealism On the other hand,]] [[{{Railroading}} this makes it impossible to]] [[AcceptableBreaksFromReality 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 took it UpToEleven by having you research the majority of the technologies in any given age before you could research ''any'' technologies in the next age.
* The base ''SpaceEmpires'' games already have sizable tech trees that grow larger with every iteration of the game. They are also quite [[GameMod moddable]], and modders have created veritable jungles of tech trees s a result.
* ''SwordOfTheStars'' has a large interconnected TechTree. 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 ''VideoGame/MasterOfOrion'' 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. [[GameBreaker Creative]] races get ''everything'' for the same price a regular race pays for one item.
* Players in ''Videogame/StarRuler'' 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, [[LensmanArmsRace otherwise you'll be left behind while other players are building]] [[PlanetSpaceship starships the size of planets]], ships that can carry [[ClownCar bigger ships inside themselves]], and [[StarKilling killing stars]].


[[/folder]]

[[folder: Hack And Slash ]]

* This can also be seen in ''VideoGame/{{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.

[[/folder]]

[[folder: MMORP Gs ]]

* Each ''WorldOfWarcraft'' class has its own, specialized tech tree, with abilities that can only be gained by putting points into it. One point per level gained from level 10 onwards.
** Now one for every other level, to cut down and the number of compulsory but boring and "increases your X damage by Y%" talents.
*** Now one for every 15 levels--you pick one of three, and cannot backtrack to pick up a second one from a lower tier. Intended to cut down extremely on the cookie-cutter builds.
* 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.
* ''EVEOnline'' 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.
* WorldOfTanks 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.
* Many Facebook [=MMORPG=]s require you to research various technologies. All of Kabam's games have it, and so do games like Wasteland Empires, though Zynga's games don't have it as much.

[[/folder]]

[[folder: Real Time Strategy ]]

* ''VideoGame/AgeOfEmpiresIII'' 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.
* ''Hegemonia: 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 [[http://guide.wz2100.net/r/tech-tree absolutely crazy about this]], since it has several hundred techs, probably range up to thousands, to be researched. Good thing it averts ReinventingTheWheel.
* Creator/ParadoxInteractive has tech trees that tends to be rather complex.
** ''VideoGame/EuropaUniversalis'' 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.
** ''VideoGame/HeartsOfIron 2'', set during WorldWarTwo, 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.
** ''VideoGame/VictoriaAnEmpireUnderTheSun'' 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)
** ''VideoGame/CrusaderKings'' 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 ''[[http://en.wikipedia.org/wiki/Utopia:_The_Creation_of_a_Nation Utopia]]'', back in 1991, although it may have been pre-empted by [[http://en.wikipedia.org/wiki/Reach_for_the_Stars_%28computer_game%29 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).
* ''[[CommandAndConquer 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 soviets (Who also have the ability to build secondary construction units and a simple build system) Have the fastest tech rush, and often dominate early game. whereas the other extreme, the allies (Who need to stop construction to go up a tech level and have the slowest, if safest building system) are given borderline GameBreaker units to compensate.
* The ''TotalWar'' 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 TechTree 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 AcceptableBreaksFromReality, 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, so InternetBackdraft ensued.
*** 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.
* ''Videogame/EightRealms'' has researchable tech trees available via the Library or University.
* ''VideoGame/JeffWaynesWarOfTheWorlds'' has a mostly hierarchical tech tree, though some things are instead unlocked as counters, AA Guns after encountering flying machines for example.
* ''VideoGame/{{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.
* ''VideoGame/SupremeCommander'' 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".
** ''VideoGame/SupremeCommander2'' 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).
* ''DawnOfWar'': 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 DivergentCharacterEvolution: Either you pick the builing 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), along with upgrades to life for all units and 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).
* MachinesWiredForWar: 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.

[[/folder]]

[[folder: Role Playing Game ]]

* ''VideoGame/SagaFrontier'' has an absolutely immense TechTree, 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.
* 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.
* ''LegendOfMana'' 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 RandomNumberGod is merciful.
* ''VideoGame/{{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 to expand your capabilities.

[[/folder]]

[[folder: Simulation Game ]]

* ''VideoGame/{{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.
* ''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.
* Pretty-much the entire point of the open-source game ''[[http://www.emhsoft.com/singularity/ Endgame: Singularity]]'' is to research the entire TechTree while not being discovered. Sounds easy, right? Well, not in the early stages of the game. Once you have Quantum Computers, however...
* The ''NavalOps'' 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 GuideDangIt.
* The 2013 release of ''VideoGame/SimCity'' 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.
* Justified in-universe in ''VideoGame/PrisonArchitect'' as the "[[ObstructiveBureaucrat 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.
* The career mode in ''VideoGame/KerbalSpaceProgram'' 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.

[[/folder]]

[[folder: Tower Defense ]]

* Most [[HoldTheLine Tower Defense]] games require that the player first build lesser towers before gaining access to the higher-level ones. A few of the more clever ones instead have the player escalate through the TechTree by "''fusing''" their lower towers together into exponentially stronger towers that usually have some characteristics of the previous ones.

[[/folder]]

[[folder: 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.
* ''HeroesOfMightAndMagic'' 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.
* ''VideoGame/AdvancedStrategicCommand'' 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). TechLevel 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.

!!Non-video game examples:

[[/folder]]

[[folder: 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.
* ''MagicTheGathering'' has the "[[http://magiccards.info/roe/en/51.html 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 TechnologyLevels.
* ''DungeonsAndDragons'' 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. 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 RulesLawyer) 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 DumpStat 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.
* Older games using the [=FATE=] system, such as ''TabletopGame/SpiritOfTheCentury'', 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.
* ''TabletopGame/FengShui'''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.
* ''TwilightImperium'' 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.)
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