The fundamental architecture of the Internet has served us well over four decades. Nevertheless, much has changed, including the capabilities of the underlying technologies, and the primary purposes that the Internet must serve. Security at all levels has grown increasingly important to the Internet's success, and its users are more interested in high-definitional television, social networking, and voice communications than they are in remotely controlling a mainframe computer. What would the Internet architecture look like if it were redesigned to meet today's needs? What services would it offer? How would it be organized? How would the technical decisions inherent in that architecture affect and be affected by economics and public policy?