Healthy and successful cities are built out of blocks and neighborhoods. Cities are too large and varied to be regarded or run as uniform entities. Block associations are proposed to be one of the major tools that are available for stabilizing and maintaining urban neighborhoods in a fashion that is both inexpensive and responsive to the needs of local residents. While the organizing of block associations has become quite common, little is understood about one of their principal problems, that is, it has often proved difficult to maintain informal and voluntary organizations for more than a few years. Residents often form groups to solve specific problems, and do not maintain them once the immediate difficulty has been alleviated. Three classes of variables that influence maintenance and effectiveness of block organizations have been identified: (1) the organization's tactics; (2) the resources that are available in the neighborhood; and (3) the organization's structure. (Author/RLV)