The architecture of the NEAT System is presented for the first time in a detailed description document. The NEAT System defines a new architecture that changes the transport layer interface exposed to Internet applications. This architecture is now available for download from the project’s website. This document starts by laying out the terminology that will be used in NEAT. It then surveys the state of the art related to the evolution of the Internet’s transport layer. Next, the document introduces requirements for a new transport architecture, and presents the NEAT Architecture that will serve as the basis for further developments made by the project.