Privacy: the Frontier of Social Evolution seeks to establish a rigorous understanding of privacy, identity and policy; and, to recognize details of the mechanisms and relationships among these seminal concepts. Privacy and identity are complementary facets of the engagements that occur between people. Conversely, privacy and policy sit astride the boundary between an individual and aggregates of people termed societies or social orders. In the real world, the world that humans know through their physiological sensori-motor systems, people engage each other through interactions. One person's identity is a metaphorical model formed in the mind of another person through interactions. Hence, identity is defined as self from the perspective of others. Human cognition results from the mind's application of such metaphorical models to the physiological sensori-motor system. Provisioning is the invocation of interactions that create these metaphorical models through which perceptions of reality are realized. Hence, privacy is defined as the provisioning of identity. Conversely, society seeks to influence the behavior of individuals through its own metaphorical models. Hence, policy is defined as the provisioning of society. A person pursues a desired identity through assertions of personal privacy. A social order pursues its goals through policies that effectively administer the personal privacy of its members; first to arbitrate the intersection of personal privacy among individuals and second to arbitrage the infringement of the privacy of individuals to benefit society. The manner in which policy addresses privacy is a central aspect of the culture of any society. The book delves into these conceptual considerations from the perspectives of human physiology, human psychology, neuroscience and digital interaction mechanisms derived from large scale computer systems and their networks. The book then uses case law to examine these considerations within the context of the infrastructures of United States jurisprudence. This results in a number of new, rather significant insights into contemporary American culture. Specifically, it is suggested that a comprehensive national identity system is a fundamental requirement for ensuring personal privacy in modern society. The book concludes with a proposal for such a system to be deployed under the auspices of the United States Postal Service.