Employed quantitative and qualitative data in a contextual examination of participation in three San Francisco-area HIV/AIDS organizations: an urban, gay community-based social change setting; an urban, broadly focused information/referral setting; and a suburban individual support setting. The settings attracted different kinds of volunteers and engaged them differently with the setting, each other, and community. In quantitative analyses external political efficacy (belief in the responsiveness of sociopolitical systems to change efforts) significantly distinguished settings, but was best predicted by setting-moderated relationships to scaled motivations. Qualitative data more clearly illuminated volunteers' motivations for participation, as well as complex, embedded relationships between setting, motivations, attitudes about sociopolitical participation, and personal and community experience and identification. Together the findings underscore three unique but related stories for the three AIDS organizations, and the value of contextual approaches to participation and empowerment.