John Yossarian is a United States Army Air Forces bombardier in World War II, furious that thousands of people are trying to kill him and that his own army keeps increasing the number of missions he must fly. He is trapped by the bureaucratic rule Catch-22, which considers a willingness to fly dangerous combat missions to be insane, yet a request to be relieved of duty on the grounds of insanity to be the process of a rational mind, so any such request must be denied.
He chose bombardier hoping the war would finish before his lengthy training but now sits exposed in the nose of a B-25 dropping bombs on strangers who are trying to kill him, unless he is avoiding flying by feigning illness, sabotaging his intercom, self-inflicted illness, or clandestinely moving the bomb line so it appears their target has already been captured.
The events occur in the Mediterranean theatre of World War II while the fictional 256th US Army Air Squadron is based on the (fictionalized) island of Pianosa, in the Mediterranean Sea, and conducting bombing raids over heavily defended fascist controlled Italy. Events are largely on base and in the air; there are later events in Italy and early scenes of basic training in the US.