I estimate that Three Strikes reduced participation in criminal activity by 20 percent for second-strike eligible offenders and a 28 percent decline for third-strike eligible offenders. However, I find two unintended consequences of the law. First, because Three Strikes flattened the penalty gradient with respect to severity, criminals were more likely to commit more violent crimes. Among third-strike eligible offenders, the probability of committing violent crimes increased by 9 percentage points. Second, because California's law was more harsh than the laws of other nearby states, Three Strikes had a "beggar-thy-neighbor" effect increasing the migration of criminals with second and third-strike eligibility to commit crimes in neighboring states.