The blockchain could be the most consequential development in information technology since the Internet. Created to support the Bitcoin digital currency, the blockchain is actually something deeper: a novel solution to the age-old human problem of trust. Its potential is extraordinary. Yet, this approach may not promote trust at all without effective governance. Wholly divorced from legal enforcement, blockchain-based systems may be counterproductive or even dangerous. And they are less insulated from the law's reach than it seems. The central question is not how to regulate blockchains but how blockchains regulate. They may supplement, complement, or substitute for legal enforcement. Excessive or premature application of rigid legal obligations will stymie innovation and forego opportunities to leverage technology to achieve public policy objectives. Blockchain developers and legal institutions can work together. Each must recognize the unique affordances of the other system.