If the existing puzzles of new financial technology—or fintech—were not enough, regulators must now confront an even deeper challenge: blockchain-based decentralized finance, or DeFi for short. DeFi services use cryptocurrencies and smart contracts to recreate traditional financial instruments and generate new ones. They promise a dynamic, disintermediating revolution in finance. And because they employ decentralized permissionless blockchains as their settlement layer, DeFi platforms are open to anyone with access to cryptocurrencies. DeFi promises significant benefits, including democratized access to financial products, improved market efficiency, easier access to liquidity, enhanced financial privacy, and faster innovation. DeFi, howe...