|Country of origin||United States|
|Headquarters location||Ann Arbor, Michigan|
|Key people||Greg Stafford, Sandy Petersen, Rick Meints, Jeff Richard, , Michael O'Brien|
|Publication types||Games, Books|
|Fiction genres||Role-playing games, Board games, Fantasy fiction, Horror fiction, Weird fiction|
|No. of employees||16|
Chaosium Inc. is a publisher of tabletop role-playing games established by Greg Stafford in 1975. Chaosium's major titles include Call of Cthulhu based on the horror fiction stories of H. P. Lovecraft, RuneQuest Glorantha, Pendragon, based on Thomas Mallory's Le Morte d'Arthur, and 7th Sea, "swashbuckling and sorcery" set in a fantasy 17th century Europe.
Many of Chaosium’s product lines are based upon literary sources. While Stafford himself has been described as "one of the most decorated game designers of all time"[better source needed] and "the grand shaman of gaming",[better source needed] many other notable game designers have written material for Chaosium. These include David Conyers, Matthew Costello, Larry DiTillio, David A. Hargrave, Rob Heinsoo, Keith Herber, Jennell Jaquays, Katharine Kerr, Reiner Knizia, Charlie Krank, Robin Laws, , , Steve Perrin, Sandy Petersen, Ken Rolston, Ken St. Andre, Jonathan Tweet, John Wick and Lynn Willis, among others.
1975–1980: Early years
Greg Stafford founded "The Chaosium" in 1975, deriving the name partly from his home, which was near the Oakland Coliseum, combining "coliseum" with "chaos". His purpose was to publish his first board game White Bear and Red Moon (later renamed Dragon Pass), a board game set in his fantasy world of Glorantha.
In 1978 Chaosium published Steve Perrin's roleplaying game RuneQuest, set in Stafford's mythic fantasy setting Glorantha, following up with a second edition in 1980 and various supplements over the next six years.
1980s: Growth and licensing with Avalon Hill
In 1980, the company officially incorporated as Chaosium Inc. That year, Stafford and Lynn Willis simplified the RuneQuest rules into the 16-page Basic Role-Playing (BRP). These simulationist, skill-based generic rules formed the basis of many of Chaosium's later "d100" RPGs, most notably Call of Cthulhu, first published in 1982.
Chaosium entered into a licensing agreement with Avalon Hill in 1983 to produce a third edition of RuneQuest. Avalon Hill manufactured and marketed the game, while Chaosium was responsible for acquisitions, design, development and layout. Ken Rolston managed the line as "Rune Czar".
Late 1990s–early 2010s: Financial struggle
In 1998, following the financial failure of the collectible card game Mythos, Greg Stafford resigned as Chaosium president and left the company, along with Sandy Petersen (although they both remained shareholders). Chaosium effectively split up into various successor companies, each maintaining its focus on a few of the company's products. Stafford took the rights to his game setting Glorantha, setting up the company Issaries, Inc. to continue publishing this line (later licensing it to Moon Design Publications, along with the game HeroQuest).
Long-time employees and part-owners Charlie Krank and Lynn Willis remained at Chaosium as President and Editor-in-Chief respectively, continuing on with Call of Cthulhu as the main product line. Lynn Willis retired in 2008 due to poor health and died in 2013.
Mid 2010s: The return of Stafford and Petersen
Problems and delays fulfilling the Kickstarters for the 7th edition of Call of Cthulhu led Stafford and Petersen to return to an active role at Chaosium in June 2015. Charlie Krank subsequently left the company.
Later that year at Gen Con 2015, Stafford and Petersen announced Moon Design Publications were now part of the Chaosium ownership, and the four principals of Moon Design (Rick Meints, Jeff Richard, Michael O'Brien and ) had become the new Chaosium management team. Chaosium once again became the licensed publisher for RuneQuest, HeroQuest and other products related to Gloranthan universe, and continue to publish the Call of Cthulhu line. Stafford and Petersen remained as board members (Stafford as chair), and creative consultants to the company.
As part of its financial reorganization, the new management closed the company office and warehouse in Hayward, California, ending Chaosium's long association with the San Francisco Bay Area. The company is now based in Ann Arbor, Michigan and uses a fulfillment house model for distribution of product.
Delivery of the core rewards of the Call of Cthulhu 7th Edition Kickstarter finally commenced in April 2016. The new edition went on to win nine of the ten awards it was nominated for at the Gen Con 2017 ENnie Awards.
On April 2, 2019, Chaosium announced they acquired the rights to the 7th Sea product line (both Second Edition and Khitai Kickstarters) from John Wick, including back stock of books published so far. 
Chaosium began publishing a line of non-game books (primarily fiction) in 1993. Many titles are themed around H. P. Lovecraft's Cthulhu Mythos and related topics, although the first work published was Greg Stafford's fantasy work King of Sartar, set in his mythic world Glorantha.
In May, 2017, Chaosium appointed award-winning author and editor James Lowder as executive editor of fiction. Lowder had previously served as a consultant for Chaosium, helping the company and freelancers resolve payment and contract problems with past fiction projects.
Although not published by Chaosium, the ongoing Wild Cards series of superhero science fiction originated from a long-running Superworld campaign gamemastered by Game of Thrones author George R. R. Martin and his circle of fellow writers who played in his game.
Three magazines have been published by Chaosium to promote its products:
- Wyrm's Footnotes ran for fourteen issues from 1976 to 1982. For the first ten issues, it was a source of supporting material for White Bear and Red Moon. In 1981, starting with Issue #11, it became the official RuneQuest magazine. The last edition published during its initial run was Issue #14, dated April 1982. The magazine was revived in 2012 by Moon Design Publications, continuing the issue numbering at 15, despite the 30-year hiatus. Issues 1 to 14 were republished in PDF format in 2019.
- Different Worlds. Forty-seven bimonthly issues from Different Worlds were published. Chaosium, from 1979 to 1985, published the first thirty-eight and , from 1985 to 1987, the final nine. Tadashi Ehara was the editor of the magazine during the periods concerned by both publishing houses.
- , a Lovecraft-themed magazine, three issues of which Chaosium published in 1997.
- "Fictitious Business Name Statement 1975". Twitter. Twitter.com. Retrieved 31 August 2020.
- "About Us". Chaosium Inc. Archived from the original on 12 October 2019.
- "Prince Valiant® Storytelling Game by Greg Stafford". kickstarter.com. Retrieved 18 November 2016.
- "Interview with Robin D. Laws". Juegos y Dados. 19 July 2016. Retrieved 18 November 2016.
- Shannon Appelcline (2014). Designers & Dragons: The '70s. 1 (2 ed.). Evil Hat Productions. p. 267. ISBN 978-1-61317-075-5.
- Varney, Allen (February 1997), "Inside the Industry", The Duelist (#15), p. 84
- "Call of Cthulhu 7th Edition". Kickstarter. Retrieved 11 June 2015.
- Michael O'Brien (30 July 2015). "Greg Stafford Announces New Ownership Group For Chaosium At Gen Con". Chaosium Blog. Retrieved 18 November 2016.
- "Chaosium Leaves California". Yog-Sothoth. 23 September 2015.[permanent dead link]
- Ben Riggs (29 April 2016). "Cthulhu Company Kickstarted itself to Death, Then This Happened". Geek and Sundry.
- "2017 Noms and Winners". ENnie Awards. Archived from the original on 2018-03-17. Retrieved 2018-03-17.
- O'Brien, Michael (2 April 2019). "John Wick joins Chaosium". Chaosium press release. Retrieved 3 April 2019.
- "2016 World Fantasy Awards Finalists". Locus Online News. 10 July 2016. Archived from the original on 2016-08-19. Retrieved 18 November 2016.
- O'Brien, Michael (7 May 2017). "Chaosium appoints James Lowder as new Executive Editor of Fiction". Chaosium (Press release). Retrieved 28 July 2017.
- O'Brien, Michael (26 August 2015). "Chaosium Appoints James Lowder as new Consulting Editor for Fiction". Chaosium (Press release). Retrieved 28 July 2017.
- Shannon Appelcline (2011). Designers & Dragons. Mongoose Publishing. p. 87. ISBN 978-1-907702-58-7.
- "Wyrm's Footnotes Submissions". chaosium.com. Chaosium. 2017-09-06. Retrieved 2020-07-12.
- "Glorantha Magazine Indices". Erzo.org. Retrieved 18 December 2014.
- Rolston, Ken (July 1983). "Companion fills the Glorantha gap". Dragon. TSR, Inc. (75): 70.
- "Different Worlds Magazine Cover Listing - RPGnet RPG Game Index". Index.rpg.net. Retrieved 18 December 2014.
- "Starry Wisdom Issue 1". www.chaosium.com. Archived from the original on 2015-03-16. Retrieved 2015-08-25.
- "Bits and Mortar: Who Are We". Publishers Who Support Bits and Mortar