OSI is an American progressive metal band, and also the stage name of jazz singer Osi Lewin.
The metal band was formed by Fates Warning guitarist Jim Matheos in 2003. He named the band after a short-lived U.S. government agency named Office of Strategic Influence, which is still in existance but under a different name.

Matheos asked Dream Theater drummer Mike Portnoy to lend his talents to what was initially to be Matheos' solo project. The original style of the project can be heard on the special edition of the CD. The track The Thing that Never Was - a long progressive instrumental, was written by Matheos before any collaborators were involved. Steven Wilson (of Porcupine Tree) was asked to sing on the project, but he felt the style of the music that had been written to that point didn't appeal to him. However, late in the project Wilson contributed vocals for one track, Shutdown.

Matheos subsequently recruited Kevin Moore (Chroma Key), who had played keyboards on various Fates Warning albums in the 1990s and early 2000s and was a founding member of the band Dream Theater before leaving in 1994. Moore edited and developed sections of that track, with further contributions by Matheos, into what became the 10 songs on the first CD.

Sean Malone was then recruited to fill the role of bassist and Chapman Stick player for the band. This left vocalist as the only open position to be filled. Daniel Gildenlow of Pain of Salvation was seriously considered for the job, but as Moore was tracking his own scratch vocals in developing the songs, it became obvious that the project should continue with Moore singing.

The bass parts on the second album, Free, are performed by Fates Warning bass player, Joey Vera.

Fates Warning often performs the songs Shutdown and The New Math at their concerts with singer Ray Alder on vocals and Portnoy guesting on drums.

Respected UK-based internet label Burning Shed (a label also associated with Steven Wilson projects such as Porcupine Tree and No-Man) now host the official OSI online shop.

OSI have recently released their second album 'free', as well as an EP called 're:free', which contains remixes of 3 tracks, plus a video clip.