Book excerpt: Housing finance markets have been changing dramatically in both emerging and developed economies. On the one hand, housing finance markets are expanding and represent a powerful engine for economic growth in many emerging economies. However, the unfolding sub-prime mortgage crisis highlights the risks and potential turbulence that this sector can introduce into the financial system when expanding without proper infrastructure and regulation. As housing finance keeps growing in emerging economies to match a rising demand for housing, new risk management approaches, business models, funding tools, and policy instruments can help. Yet many questions remain about the right balance between innovation and regulation, the extent of risks to the financial system, the appropriate role of the state to promote affordable housing, and the effects of the sub-prime crisis. This book provides a guide for policymakers dealing with housing finance in emerging markets. It highlights the prerequisites for an effective housing finance system; it lays out several policy alternatives and models of housing finance; and it explores the role of governments in expanding access to housing finance for lower-income households. There is no "best" model set out in this book. The aim is to provide a developmental roadmap that can be tailored and sequenced to each country's situation and timing.