This article presents an ecological perspective on homelessness that emphasizes the context in which homeless people live and the complex interactions between personal, social, economic, and service system resources that affect their well-being. The ecological perspective encourages researchers and program developers to assess the problems of homelessness at multiple levels of analysis, to view homelessness as a result of contextual factors that interact with individual and family vulnerabilities, and to assess carefully the social contexts in which researchers and program developers operate. Four ecological principles are described as a heuristic for research, intervention, and policy development. The implications of an ecological perspective for psychologists who wish to get involved in dealing with homelessness are discussed.