Irrational Games was founded in 1997 in Quincy, Massachusets by Ken Levine and several of his co-workers who have previously worked in other fields of the gaming industry. In the early years, Irrational was in many ways the sister company of Creator/LookingGlassStudios. They even exchanged their employees quite frequently and co-developed several projects (until LGS' closure in the spring of 2000). Over the years, Irrational Games have published a number of critically acclaimed and commercially succesful games - particularly the famous second installment of the ''VideoGame/SystemShock'' series, ''VideoGame/{{SWAT 4}}'' and the ''VideoGame/BioShock'' series (a {{spiritual successor}} to the original ''VideoGame/SystemShock''). In the early 2000s, the company opened up an Australian studio in Canberra.

In January 2006, Irrational was bought by Creator/TakeTwoInteractive and its name was changed to 2K Boston, with its Australian studio becoming 2K Australia. In 2010, however, Take-Two had a change of heart and allowed 2K Boston to adopt its former name again (seeing it as having better brand-recognition potential, given the succesful history of the developer). The Australian studio was eventually separated from Irrational and became a part of 2K Marin.

Their most recent project was the very successful ''VideoGame/BioShockInfinite'', the third installment of the series, which featured a brand new story and {{steampunk}}ish enviroments.

In February 2014, Levine announced on the company's website that he would "wind down Irrational Games as you know it" in an effort to focus on smaller, narratively driven games distributed digitally under the Take Two umbrella. This process entailed laying off most of the company and putting together a much leaner team of developers and was finalized in early 2017, with the founding of Creator/GhostStoryGames, a team of roughly two dozen developers led by Levine. As of that moment, Irrational Games has been effectively defunct.

Their website can be found [[http://irrationalgames.com/ here]]. They also have a podcast, called ''[[http://irrationalgames.com/insider/irrational-behavior/ Irrational Behavior]]''.

!!Games developed:
* ''VideoGame/SystemShock 2'' - Due to this being a collaboration with Creator/LookingGlassStudios, the game even uses the same basic engine as the first two ''VideoGame/{{Thief}}'' games.
* The ''VideoGame/FreedomForce'' series
* ''[[{{VideoGame/TribesVengeance}} Tribes: Vengeance]]'' -- A prequel to the ''{{VideoGame/Tribes}}'' series & sequel to the ''{{VideoGame/Starsiege}}'' series.
* ''VideoGame/{{SWAT 4}}'' - The fourth installment of {{Creator/Sierra}}'s tactical shooter series.
* The ''VideoGame/BioShock'' series

!!Tropes about this developer:
* DevelopersForesight: Irrational are well-known for their thoroughly in-depth gameplay mechanics that account for a lot of different situations the player can find himself in.
* SophisticatedAsHell: The below original pitch for Bioshock lists "scare the hell out of people" as one of the primary objectives. This is the only instance of swearing in the document, which is otherwise extremely professional.
* WhatCouldHaveBeen: Lots of examples of this in the company's history. The [[http://irrationalgames.com/insider/ Insider section]] of the studio's website [[http://irrationalgames.com/insider/from-the-vault/ gradually reveals]] a lot of them, mostly unrealized ideas or unused concept art.
** ''VideoGame/SystemShock II'' was originally suppossed to feature a level set outside the ship, in the vacuum of space. It proved technically too demanding for the Dark Engine and the idea was eventually droped.
** The [[http://irrationalgames.com/insider/from-the-vault-may/ original]] [[http://irrationalgames.com/insider/from-the-vault-june/ pitch]] for ''VideoGame/BioShock1'' had a ''very'' different setting, backstory and plot.
** [[http://irrationalgames.com/insider/irrational-behavior/introducing-irrational-behavior/ Sometime]] [[http://news.bigdownload.com/2010/01/12/irrational-reveals-canceled-zombie-game-division-9/ in late 2005]] [[http://www.youtube.com/watch?v=IyRlau2WwXY and early 2006]], Irrational Games used the existing ''SWAT 4'' engine and assets as a proof-of-concept basis for their next game project, preemptively titled ''Division 9''. It was supposed to be a SurvivalHorror shooter with a squad-based nature (much like SWAT 4) and set in... a noirish city after a mysterious ZombieApocalypse. The project was eventually scrapped in favour of concentrating on ''VideoGame/BioShock1''. Three years later, Valve published [[VideoGame/Left4Dead a game with the same basic idea]]. Makes you wonder if ''Division 9'' would've been similarly succesful years ago...
** ''VideoGame/BioshockInfinite'' had gone through a lot of different concepts. WordOfGod even noted that the team had to cut "five or six games" worth of material from the final product.
** ForWantOfANail: Had [[https://en.wikipedia.org/wiki/Voyager_%28video_game%29 an adventure game based on]] ''Series/StarTrekVoyager'' not been cancelled by Viacom when Creator/LookingGlassStudios was developing it in the mid 1990s, Ken Levine, Jonathan Chey and Rob Fermier might not have left the studio to found Irrational Games.