An architectural principle known as protocol layering is widely recognized as one of the foundations of the Internet’s success. In addition, some scholars and industry participants have urged using the layers model as a central organizing principle for regulatory policy. Despite its importance as a concept, a comprehensive analysis of protocol layering and its implications for Internet policy has yet to appear in the literature. This Article attempts to correct this omission. It begins with a detailed description of the way the five-layer model developed, introducing protocol layering’s central features, such as the division of functions across layers, infor- mation hiding, peer communication, and encapsulation. It then discusses the model’s implications for whether particular functions are performed at the edge or in the core of the network, contrasts the model with the way that layering has been depicted in the legal commentary, and analyzes attempts to use layering as a basis for competition policy. Next the Article identifies certain emerging features of the Internet that are placing pressure on the layered model, including WiFi routers, network-based security, modern routing protocols, and wireless broadband. These developments illustrate how every architecture inevitably limits functionality as well as the architecture’s ability to evolve over time in response to changes in the technological and economic environment. Together these considerations support adopting a more dynamic perspective on layering and caution against using layers as a basis for a regulatory mandate for fear of cementing the existing technology into place in a way that prevents the network from innovating and evolving in response to shifts in the underlying technology and consumer demand.