This chapter reviews the nascent empirical literature on copyright registrations at the U.S. Copyright Office. In one body of work, scholars explored patterns of use of the copyright system. Individuals and corporations tend to register different types of works, of different published status, at different rates, times and locations. Individual authors of different races, genders and ages similarly tend to register different types of works at different rates. In a second body of work, noisy registration data were used to measure the effect of various statutory revisions and court precedents on creativity. The chapter discusses the promise and challenges of using registration data to guide copyright law reform.