Twenty-five years ago Richard Epstein published Simple Rules for a Complex World, which would go on to become one of Epstein’s most influential works. This essay, prepared for a conference and symposium to celebrate the anniversary of the book, applies the insights of Simple Rules in the context of one of the most complex areas of social and economic regulation, financial regulation. The complexity of modern finance is often thought to require an equally complex regulatory structure to preserve the safety of the financial system and thus Epstein’s approach is inapplicable to this context. We argue that this argument is exactly backwards. Simplicity in the regulatory framework is essential for financial institutions to manage risk and conduct their affairs efficiently and prudently. Complexity, by contrast, begets a variety of destabilizing problems, including the likelihood of regulatory arbitrage and errors by regulators that increase risk. We argue that refashioning financial regulation around Epstein’s concept of simple rules would create a more stable and efficient financial regulatory system.