I develop a simple model of banks that includes financial regulations and systemic risk. It is utilized to examine the effects of five possible taxes (on bank loans, deposits, liabilities, equity, and profits), and I discuss extensions to consider depositor access to international capital markets and tax avoidance by multinational banks. The model emphasizes systemic risk in a bank’s loan choice. An externality arises because a bank’s loan decisions affect the economy-wide probability of loan success. The bank takes account of the effect of its loan decisions on itself but ignores the effects on other banks in the system.