iO, or iO Chicago, (formerly known as "ImprovOlympic") is an improv theater and training center in central Chicago, with a branch in Los Angeles called iO West. The theater both teaches and hosts performances of improvisational comedy. It was founded in 1981 by the late Del Close and Charna Halpern. The theater has many notable alumni, including Amy Poehler and Stephen Colbert.
iO is both a school and a theater troupe. 