When making a decision about housing, a household must choose between renting and owning. Multiple factors, such as a household's financial status and expectations about the future, will influence the decision. Few that decide to purchase a home have the necessary savings or available financial resources to make the purchase on their own. Most need to take out a loan. A loan that uses real estate as collateral is typically referred to as a mortgage. Historically, the government has played an important role in the housing finance system providing both support to the system and regulation of it. The housing finance system has two major components: a primary market and a secondary market. Lenders make new loans in the primary market, and loans are bought and sold in the secondary market. This book provides an overview of how the housing finance system works and provides context for housing finance-related policy issues that Congress might choose to consider.