Many communities are developing innovative forms of collaborative organizations such as multi-sector health care alliances (MHCAs) to address problems of misaligned incentives among providers, payers, and community stakeholders and improve health and health care. Member engagement is essential to the success of these organizations due to their dependence on volunteer members to develop and implement strategy and provide material and in-kind support for alliance efforts, yet relatively little research has examined how alliances can foster engagement. This study examined behavioral indicators of member engagement (e.g., recruitment and retention of organizational and individual members) and how they are related to two foundational dimensions of alliance functioning – alliance leadership and community centrality. Using three rounds of an internet-based survey of alliance members from 14 alliances, the study found that organizational recruitment and retention increased over time, from 26.6% to 41.5% and 56.0% to 65.2%, respectively. Recruitment of individuals increased over the study period (38.3% to 47.2%, while retention of individual members declined over the study period (61.0% to 53.2%). Alliance leadership was associated with lower levels of recruitment (both organizational and individual members) but higher levels of organizational retention (both organizational and individual members). Collectively, our findings suggest that behavioral aspects of alliances are more effective at retaining members than relatively stable characteristics such as size and positioning in the community. Contrasting relationships between recruitment and retention, however, suggest that different forms of leadership may be required to simultaneously attract new members while retaining existing ones.