California is one of eight states that have established a “millionaire tax” in recent years. The popular appeal of these taxes is that they raise revenue from those seen to have greater ability to pay a higher rate on the highest portion of their incomes. The concern, however, is that millionaire taxes may lead to millionaire migration, with potentially serious loss of revenues for the state. This study addresses the following key question: Do changes in California’s top income tax rates lead to changes in the migration of top incomes?