The question of what effect formal structures of neighborhood organizations have on member involvement has largely been ignored in the body of research on neighborhood politics. Yet mandatory and voluntary neighborhood organizations have proliferated in recent years, motivating this research to address the gap in the extant literature. Findings based upon 164 neighborhood organizations surveyed in Houston, Texas, indicate that mandatory organizations are stronger than voluntary organizations in terms of financial capability, bureaucratization, member size and percent of neighborhoods formally represented, while voluntary organization structures are more democratic. Furthermore, the analysis supports the contention that decentralized participation structures and change oriented purposes and incentive structures significantly increase the proportion of members involved in the activities of the neighborhood organizations surveyed.