In the aftermath of the recent financial crisis, a variety of taxes on financial institutions have been proposed or enacted. The justifications for these taxes range from punishing those deemed to have caused or unduly profited from the crisis, toaddressing the budgetary costs of the crisis, to better aligning banks’ and bank executives’ incentives in light of the broader social costs and benefits of their actions. Although there is a long-standing literature on corrective, or Pigouvian, taxation, most of it has been applied to environmental externalities, and the externalities that arise from the actions of financial institutions are structurally different. This paper reviews the justifications for special taxes on financial institutions, and addresses what kinds of taxes are most likely to achieve the various stated objectives, which often are in conflict. It then critically assesses the principal taxes that have been proposed or enacted to date: financial transactions taxes, bonus taxes, and taxes on firms in the financial sector based on size, bank liabilities, or excess profits.