OSI is an American progressive rock band, originally formed by Fates Warning guitarist Jim Matheos in 2002. Chroma Key keyboardist and vocalist Kevin Moore is the only other full-time member of the band. The collaboration may be considered a studio project, as its members and contributors write and track most of their material independently, sharing and developing tracks long-distance, only coming together at the end of the process for mixing and additional tracking. The band's name is a reference to the Office of Strategic Influence, a short-lived American government agency formed in 2001 to support the War on Terror through propaganda. The band has featured a number of guest musicians on its albums, including Sean Malone, Steven Wilson, Mikael Åkerfeldt, Joey Vera and Gavin Harrison.

Matheos recruited Moore, Dream Theater's then-drummer Mike Portnoy and Sean Malone (Fretless Bass and Chapman Stickist) to perform on what was originally planned to be a Matheos solo album. Matheos and Portnoy originally planned to produce a progressive metal album similar to Matheos' work in Fates Warning, however Moore's impact changed the music's direction and genre, incorporating electronica into the original progressive metal sound. The band's debut album was released by InsideOut Music in 2003.

OSI was originally intended to be a one-off project, but Matheos and Moore found they both had gaps in their schedules so produced a follow-up. Free was released in 2006, with Portnoy returning to play drums as a session musician rather than a full band member, due to personal and musical differences between him and Moore. Blood was released in 2009, with Porcupine Tree drummer Gavin Harrison replacing Portnoy. The fourth album Fire Make Thunder was released in 2012 by Metal Blade Records, with Harrison once again on drums.