Costikyan's notable works include
- Toon
- The Roleplaying Game (Origins Award Winner for Best Role-playing Rules of 1987)
- Pax Britannica (Charles S. Roberts Award Winner for Best Pre-20th Century Game of 1985)
- Paranoia (Origins Award Winner for Best Roleplaying Rules of 1984)
- The Creature That Ate Sheboygan (Charles S. Roberts Award Winner for Best Fantasy or Science Fiction Game of 1979)
- MadMaze
- The Roleplaying Game of Egregious and Repulsive Bloodshed
In addition, Costikyan is a widely-published author on the subject of game design and the role of games in culture. His essay, "I Have No Words and I Must Design"is widely read as a conceptual approach to framing game design.
Costikyan worked on game design for many years, including writing and consulting for Nokia. In September 2005, he left Nokia to join with Johnny Wilson, former editor of
Computer Gaming World, in founding the startup indie game publisher Manifesto Games.He regularly contributes to Manifesto Games' website, and to their offshoot game review blog Play This Thing.
In the 1970s and 80s, Costikyan was a leading player of Slobbovia. His novel
One Quest, Hold the Dragons includes several stories about crottled greeps, a Slobbovian meme.
In February 2009, Costikyan updated the rules and re-released his 1979 space combat game, Vector 3, under a Creative Commons license as a free PDF download.