This article summarizes the findings of a study of community-wide strategies for preventing homelessness among families and single adults with serious mental illness, conducted for the US Department of Housing and Urban Development. The study involved six communities, of which this article focuses on five. A major finding of this study was that it was difficult to identify sites with community-wide strategies, and even harder to find any that maintained data capable of documenting prevention success. However, the five communities selected for this study presented key elements of successful strategies including mechanisms for accurate targeting, a high level of jurisdictional commitment, significant mainstream agency involvement, and mechanisms for continuous system improvement. (Authors)