These efforts involve large-scale intervention and social-change strategies in urban areas that attempt to provide opportunities to disadvantaged youth, develop community resources, implement institutional reform, and organize and mobilize target-area residents for collective action. The author uses a typology of community organization practice developed by Jack Rothman to analyze the assumptions, objectives, and methods underlying these kinds of programs. Rothman identified three general models of community organization practice: locality development, social planning, and social action. This chapter uses these models to evaluate three exemplary delinquency prevention programs: the Chicago Area Project, the 1960's provision of opportunity programs, and the 1960's comprehensive community action projects such as Mobilization for Youth. These programs spanned a range of local and Federal efforts that emphasized alteration of neighborhood, institutional, and economic conditions that were believed to cause delinquency. After outlining the assumptions underlying the three practice models and evaluating the delinquency prevention programs, the chapter also considers implications for contemporary crime prevention efforts. The author concludes that in spite of the difficulties that confront future primary prevention efforts, the projects reviewed in this chapter show that it is possible to design and implement an effective strategy that mobilizes the entire community to address the delinquency problem. Greater attention should be given to the possibilities and limitations inherent in using the locality development, social planning, and social action models of community organization practice. 15 notes and 92 references