Blue Team was the designation given by the UNSC to a team of Spartans led by Johnny-117, which fought during the Human-Covenant War. At the start of the war the team was almost 15 strong, but by the end of the war only 4 Spartans from the team remained in active service.
Following his many misadventures at the end of the war and after his experiences with Jorgey on Requiem, Johnny sought out his old team and got the band back together, only to lead them all into AWOL status after suffereing a mental breakdown, partly due to the realisation that Cortana was evil but mostly due to Jorgey's lingering effects.
After this, Blue Team travelled around the Galaxy from Meridian to Genesis, all the time being chased by ONI's Fireteam Osiris, who sought to bring them home. Eventually, Blue Team and Osiris teamed up to oppose Cortana and both teams allied with Arby's forces to form a supreme alliance.