This paper surveys research on homelessness. The emphases are on the last decade, rather than earlier; and the United States, rather than the rest of the world. The approach is more idiosyncratic than encyclopedic. The field has been converging on the conclusion that housing subsidies are the most attractive policy for reducing homelessness, but the optimal arrangement of subsidies is not obvious. Economists have much to contribute, in both theory—mechanism design and general equilibrium—and empirics. Aggregate-level studies can be used more for finding out what the effects of different policies are, and individual-level studies can be used more for assessing the costs and benefits of those effects.