Homelessness and Housing Exclusion in Europe: Challenges and Opportunities for Research and Policy The European Parliament recently passed a Written Declaration “calling for an ambitious EU homelessness strategy and support to Member States in their efforts towards ending homelessness” (FEANTSA, December 21, 2010). The Written Declaration comes on the heels of a consensus conference on homelessness held in Brussels, in which researchers from the European Observatory (some featured in this volume) made the moral and empirical case for urgent and strategic action by all member countries of the EU. This leadership has proven to be critically influ- ential as the European Commission moves forward with its antipoverty goals for 2020. This timely volume will help bring further momentum to this cause, by framing much of what has been learned, and many of the important questions yet to be addressed in this highly complex, multinational context. Among researchers and policymakers, the overall direction for homelessness policy – expanding access to stable and affordable housing, with appropriate supports – seems now to be a consensus opinion. Beyond that, the details necessary for a coherent pan-European homelessness strategy will require substantial new knowledge development. As illustrated by the chapters in this volume, researchers are engaged in the challenging work of operationalizing the homelessness problem and establishing evidence-based practices that can be scaled up in a multinational, and “multi-sociopolitical” environment. While daunting, much progress has been made. Determining exactly how to define homelessness is a crucial first step for under- standing the problem, and since its publication in 2005 the European Typology on Homelessness and Housing Exclusion (ETHOS) has offered researchers in Europe (and abroad) a thoroughly well conceptualized definition of homelessness and residential instability. In this regard, the ETHOS statement is a major achievement, and a critical starting point for comparative research and policy analysis. Nonetheless, countries have not yet fully aligned their definitions of homelessness and housing exclusion, and partly as a result, measuring the scope and extent of homelessness in Europe still remains a significant obstacle. As Volker Busch- Geertsema notes in his chapter, measurement efforts have proceeded particularly slowly when considering roofless and houseless persons, the most vulnerable categories of persons in the ETHOS typology and the groups that are most European approaches. Thus, the adaptation of the Esping-Anderson framework to homelessness here opens further an area ripe for future research, both of a qualitative and quantitative nature, and from which much is yet to be learned.