This Article examines how the prevailing legal conception of privacy facilitates the erosion of privacy. The law generally measures privacy by reference to society’s reasonable expectation of privacy. If we think of the universe of legally private matters as a sphere, the sphere will contract (or least in theory) expand in accordance with changing social expectations. This expectations-driven conception of privacy in effect establishes a privacy marketplace, analogous in both a literal and metaphorical sense to a marketplace of ideas. In this marketplace, societal expectations of privacy fluctuate in response to changing social practices. For this reason, privacy is susceptible to encroachment at the hands of large institutional actors...