In this review, I examined the last two decades of research on data use in education to outline the ways in which principals used data to inform their own leadership practices. I found three themes: first, student achievement data were the most widespread form of data that principals used; second, principals' work has been reshaped by teacher evaluation reform, especially with respect to their use of data for human capital management; and finally, personal characteristics and organizational conditions played an important role in shaping principals' data use. I conclude by proposing a research agenda for the field.