The Metropolitan Transit Authority regulates busking—playing music or performing for tips in a public place—differently depending on the subway station. Some stations are reserved for members of a program called Music Under New York (MUNY), while at the others, anyone willing to pay the standard fare to enter the station is allowed to busk. As it happens, the distribution of MUNY and non- MUNY stations within the subway system follows an economic pattern. MUNY covers the stations where we should expect busking to impose the highest externality costs. This economic pattern of coverage provides the substantive basis for this Note: Because MUNY’s distribution is consistent with Harold Demsetz’s foundational theory about the economic development of private property rights, MUNY provides a window into a question left open by Demsetz and contested in subsequent literature—the question of how private property develops. This Note analyzes MUNY to make two contributions to the growing body of literature describing how property rights develop. First, observing the role that changing First Amendment doctrine played in MUNY’s formation, this Note argues that exogenous legal norms act as constraints on the mechanisms through which new property rights develop. Second, it argues that Demsetz’s theory should take account of the inertia built into property systems and the external shocks that help overcome this stasis.