Judicial self-restraint, once a rallying cry for judges and law professors, has fallen on evil days. It is rarely invoked or advocated. This Essay traces the rise and fall of its best-known variant—restraint in invalidating legislative action as unconstitutional—as advocated by the “School of Thayer,” consisting of James Bradley Thayer and the influential judges and law professors who claimed to be his followers. The Essay argues, among other things, that both the strength and the weakness of the School was an acknowledged absence of a theory of how to decide a constitutional case. The rise of constitutional theory created an unbearable tension between Thayer’s claim that judges should uphold a statute unless its invalidity was clear beyond doubt (as it would very rarely be), and constitutional theories that claimed to dispel doubt and yield certifiably right answers in all cases.