Catch-22 is Joseph Heller's best known novel, and a masterpiece of American literature. It is his expression of the futility, frustration, and utter chaos behind war. The book's characters, (especially Yossarian) spend whole of the book trapped in a series of weird situations that they are unable to explain, rectify, or even understand. The phrase "Catch-22" is basically a reference to a supposed law that covers The Army's Big Olive Drab Ass on almost anything it feels it needs to do, but most importantly it prevents pilots from being grounded from flight duties on the basis of insanity. If a pilot is sane enough to realize that flying is dangerous, and that pilot requests to be grounded then he is obviously sane enough to continue flying. The only way a pilot can be grounded though is by request. Tricky eh?