Governments throughout the world intervene heavily in housing markets, and most have multiple policies to pursue multiple goals.  This chapter deals with two of the largest types of housing policies in the United States, namely, low-income rental assistance and policies to promote homeownership through interventions in mortgage markets.  We describe the rationales for the policies, the nature of the largest programs involved, the empirical evidence on their effects, and the data and methods used to obtain them.  Because the U.S. government uses such a wide range of policies of these types, this evidence has lessons for housing policy in other countries.