->''2008, I am BACK!''
-->-- Counter-Strike Online announcement trailer.

The most popular online {{FPS}} in the world, now a MMO!

''Counter-Strike Online'' is a MMOFPS targeted towards Asia's gaming market. It is developed by Nexon Corporation of South Korea with oversight from license-holder Valve Corporation, essentially modified ''VideoGame/CounterStrike'' v1.6 with bits and pieces assets from ''Counter-Strike: Condition Zero.'' It uses a micropayment model that is managed by a custom version of the Steam back-end.

The game is originally released in various Asian countries: South Korea, Japan, Republic of China, Taiwan, Singapore/Malaysia, Indonesia and Thailand, before released in Turkey, and then released for Russia, Europe and Americas as Counter-Strike Nexon: Zombies. Aside from the same-old-same-old look of Counter-Strike 1.6 with bits and pieces of Condition Zero, Online naturally provides more original content for the game, new weapons, player models, game modes and much, much more. Some game modes are based on custom mods for the original Counter-Strike, such as Zombie Mode, Zombie Scenario Mode, Gun Deathmatch, etc.

It also has a sequel simply titled as ''Counter-Strike Online 2'', which is a beast of its on as it's built from the ground up with the Source engine, unlike its predecessor.

!!Includes examples of:
* AKA47 - Zig-zagged. Korean, Japanese and Taiwan versions, straight up calls them by their original name (i.e: AWP), but Malaysian/Singapore and Indonesian versions calls it by Condition Zero titles to ease up the localization work (i.e: Magnum Sniper Rifle). Some names are consistent between all regions, like calling the Desert Eagle as the Nighthawk .50c or the Barrett M95 as-is.
* AllegedlyFreeGame - You should see this coming, since it's a South Korean made MMO. It's a blessing that cash point items (weapons, model skins etc.) may be sold with a permanent status, which sits in your inventory forever. Not to mention that the entire CS 1.6 content, plus exclusive maps, is available for all players for free.
** Unfortunately the recent updates negated this and replaces the weapons with Confirmed Blueprints, which is crafting specifically that item with a duration. To make it permanent, 1000 Duration Extenders is needed.
* AnnouncerChatter - In tradition with the custom mods of the original, Nexon provides their own announcer chatter for both CSO and its sequel.
* AntiFrustrationFeatures - At least, Nexon Zombies is much, much more lenient and less cash-heavy compared to other countries. Play three hours a day? Receive 1 mileage decoder every one hour. Event weapons in other countries can expire? Nexon Zombies have them on permanent, without having to waste 1000 Duration Extenders for weak weapons. Only had a duration weapon or used to have them but it expired when there's a weapon upgrade event? You can have a friend throw that specific weapon and get the upgraded weapon for life. Really, there's a lot to list in this that makes the RU/EU/US version a much more favorable version for cash-strapped players.
* ArmorIsUseless - You can buy a helmet, vest, or both. They barely lessen the damage taken - they're the difference between five bullets killing you and four bullets killing you. Realistically, though, the armor is more effective against sub-machine guns and pistols (except the Deagle) than against heavier arms and also protects well against grenades. In Zombie Scenario Mode, they are effective in lessening the damage you get from the melee-ing zombies. Played straight in Human Scenario Mode, since they doesn't seem to affect the amount of hits you can take before your screen turns completely red.
* BlingBlingBANG - The gold-plated versions of regular guns quickly falls into this quickly.
* {{Bowdlerize}} - The Republic of China version is noticeably guilty for this, changing the color of blood into green. It doesn't stop there, due to the rather gruesome look of the Regular Zombie, they are replaced with the models of the Psycho Zombie which in other releases pop smoke. The proper smoke-popping Psycho Zombies are PaletteSwap. The blood-drenched gown of the host Light Zombies are clean.
** If you are playing with a juvenile Nexon account for South Korea, blood is censored and painted yellow, while the red blood in the screen for Human Scenario Mode turns dusty.
* CountrySwitch - Non-Asian version of this game is called ''Counter-Strike Nexon: Zombies''
* GatlingGood - Various man-portable M134s are available in ''[=Counter-Strike Online=]'', each with its own ability.
* GunsAkimbo - The Dual Beretta Elites are no longer the only dual-wield weapon in Counter-Strike Online. There's now dual wielding for a lot of things.
* LeeroyJenkins - Just go on the online games. ''No one'' works together, unless they're in clans.
* {{Lethal Joke Weapon}} - The C-Box exclusive Lightning Series weapons lives in this trope. Let's see, a guitar gun, a violin, two water guns, an umbrella shotgun and a lot more. There's even a currently released (purchasable) weapon which makes you hold a super-deformed, fat heavy zombie that literally ''farts'' at whoever you point and shoot.
* MoneySpider - The zombies in Zombie Scenario drops chests with various treasures inside. Troops in Human Scenario Mode gives you spoils randomly.
* PaletteSwap - Some weapons suffer from this. Christmas version, Red versions, Gold versions, etc.
** Zombies in Zombie Scenario Mode also does this, and they are slightly different depending on the color. Dark orange, green, black, and so on and so forth.
** Ditto that with the map dm_gallery and dm_kart.
* {{Qurac}} - de_dust and de_dust2, with their two variants, and the Human Scenario map, Desert Storm.
* RareGuns - And as a staple for games in this genre, weapons such as the Jackhammer, AN-94 and such exists for use. Their usefulness however varies.
* RandomNumberGod - The game's daily roulette, bingo, C-Box (lucky prize box), crafting and weapon enhancement is mostly heavy with this. The C-Box feature needs to be decoded with keys bought with cash points (i.e real money) and if you're lucky, you'd get a gold-plated weapons, exclusive reskins, rare weapons or previously-released permanent weapon. The gold weapons and reskins are not entirely useless since some of them are better than the original in spades, such as being lighter, hits harder or having more ammo.
** Mileage Decoder at least rewards use, coupled with a permanent Bingo, but the whole mechanic is still subject to this.
* RegeneratingHealth - Only in Human Scenario Mode for the bloody screen kind.
* RightHandedLeftHandedGuns - Again, zig-zagged. Certain weapons are made to mirror correctly, some doesn't.
* SawedOffShotgun - Comes in two flavors, Double Barrel and the Quadbarrel.
* {{Shoutout}} - The regenerating health feature in CSO's Human Scenario Mode is similar to those in the recent ''VideoGame/{{Call of Duty}}'' games.
** The C-Box exclusive weapon, the Dragon Claw, is [[WolverineClaws a pair of knuckle dusters with claws]].
** Some weapons have reload animations that are either similar or direct lift from a different game. The [[RareGuns MK3A1]]/Pancor Jackhammer in CSO, for example has the exact reload animation used in {{Battlefield 3}}.
* StandardFPSGuns - Until they release the anti-zombie guns and premium weapons anyways.
* SticksToTheBack - Non-gun example in the game: the Heavy Zombie's butcher knife sticks to the back when holding the zombie grenade, while the Stamper have an iron maiden on his back.
** Played straight in ''Counter-Strike Online 2'', however.
* SuperSenses - Hearing, specifically. Not just in competitive modes, improved hearing in Zombie Modes would probably save your life, if not being a ParanoiaFuel for loners and last man standing.
* TerroristsWithoutACause - Averted with the new characters. While the original models has their own goals, the more recent characters introduced in CSO is more on opposing the government because of their Super Soldier Project.
* ThrowAwayGuns - A sometimes effective strategy, both offensively (for [[LeeroyJenkins Leeroy Jenkinses]]) and defensively (No time to reload because the enemy is rushing you? Throw away your gun and grab a dead guy's gun!).
* WesternTerrorists - Militia, Arctic Avengers and Phoenix Connexion, from The US, Sweden(!) and former Soviet Union respectively, and then joined by the Vigilante Corps and the National Liberation Campaign, which are based off the IRA and ETA respectively.
* ZombieApocalypse - As a nod to the mod of the original Counter-Strike, Counter-Strike Online is blessed with three types of ZombieApocalypse game modes, Zombie Mode, Zombie Scenario Mode and Zombie Escape. Zombie Mode is basically Infection while Zombie Scenario Mode is NOTD/Zombie Riot with several changes. Zombie Escape originates from a mode of the same name from ''Counter-Strike Source''.