This study explored organizational and contextual factors impacting coalition functioning across 15 community-researcher coalitions that were formed to lower rates of HIV among youth. Mixed-methods (qualitative and quantitative) longitudinal data were collected from both community partners and researchers across three time points, and were analyzed to assess factors associated with initial coalition development and functioning. Specific facilitators of coalition functioning over time included developing group trust and cohesion, creating diverse coalition membership, developing a shared vision, and ensuring clarity of coalition purpose and goals. Specific barriers to coalition functioning over time included experiencing a lack of clarity over member roles and responsibilities, balancing power/resource dynamics between researchers and community partners, balancing coalition building and coalition pace, and experiencing HIV/AIDS-related stigma. Recommendations are offered for how to develop and sustain successful community-researcher coalitions over time in order to address relevant social issues.