Today–following housing bubbles, bank collapses, and high unemployment–the Internet remains the most reliable mechanism for fostering innovation and creating new wealth. The Internet’s remarkable growth has been fueled by innovation. In this pathbreaking book, Barbara van Schewick argues that this explosion of innovation is not an accident, but a consequence of the Internet’s architecture–a consequence of technical choices regarding the Internet’s inner structure that were made early in its history. The Internet’s original architecture was based on four design principles: modularity, layering, and two versions of the celebrated but often misunderstood end-to-end arguments. But today, the Internet’s architecture is changing in ways that deviate from the Internet’s original design principles, removing the features that have fostered innovation and threatening the Internet’s ability to spur economic growth, to improve democratic discourse, and to provide a decentralized environment for social and cultural interaction in which anyone can participate. If no one intervenes, network providers’ interests will drive networks further away from the original design principles. If the Internet’s value for society is to be preserved, van Schewick argues, policymakers will have to intervene and protect the features that were at the core of the Internet’s success.