The period 1870-1930 witnessed the emergence of the local public library as a widespread and enduring American institution. During these years, access to free community-based library services spread to a much larger share of the U.S. population, while the institutional structure of local libraries underwent a transition from largely quasi-private, voluntary associations to the tax-supported public institutions familiar today. In this paper we describe this transition, and document the expansion of public libraries and library services in the United States over these years, using data drawn from library surveys conducted by the federal Bureau of Education. We then review some causal accounts for that expansion. Exploiting cross-state and tem...