Catch-22, the book, doesn't really tell a straightforward linear story. Really, it's based on jokes, references, repetition and paradoxes. So adapting it into a movie required a lot of imagination, and in fact the movie starts at the end, with Yossarian getting stabbed. Yossarian really is crazy, and so is everyone else in the movie, but he can't get shipped home, because catch-22 says he must be sane. The movie runs through flashback after flashback until it gets back to the beginning, which is really the end, only now you understand what the hell is going on. The cast is superb, and the direction by Mike Nichols, is highly effective. Watch for the many tracking shots, which I suppose most commenters will disregard. Highly recommended.