The Credit Card Accountability, Responsibility, and Disclosure (CARD) Act of 2009 limited companies’ abilities to raise interest rates on outstanding balances on consumer credit cards, potentially reducing the incentive for companies to compete by lowering rates. Geng Li of the Federal Reserve Board and Yiwei Dou and Joshua Ronen of New York University find that, following passage of the CARD Act, competition declined significantly in the market for consumer credit cards relative to the market for small business credit cards, which were not subject to the Act. They show that prior to the CARD Act, credit card companies lowered interest rates on their cards by about ½ percentage point for every 1 percentage point that a competitor lowered rates; after the Act, that response fell to about 1/8 percentage point. The authors find that overall, the CARD Act led to higher and more varied interest rates on consumer credit cards relative to cards that were exempt from the law. The findings suggest that regulations aimed at consumer protection can have unintended effects on market competition.