Prevention has long been cited as an important part of any strategy to end homelessness. Nonetheless, effective prevention initiatives have proven difficult to implement in practice. The lack of a prevention-oriented policy framework has resulted in responses to homelessness that focus primarily on assisting those who have already lost their housing and, consequently, to the institutionalization of homelessness. Recent Federal legislation, however, signals an emergent paradigm shift towards prevention-based approaches to homelessness. This paper explores the conceptual underpinnings of successful prevention initiatives and reviews practice-based evidence from several successful prevention-oriented approaches to homelessness in the United States and Europe. We then outline a conceptual framework for a transformation of homeless assistance towards prevention oriented approaches, with a discussion of relevant issues of program design and practice, data collection standards, and program performance monitoring and evaluation.