In response to large numbers of senior center clients who suffer untreated depression and the dearth of geriatric mental health providers, the investigators have simplified a Behavioral Activation intervention to match the skill set of age-matched lay volunteers available to senior centers (Volunteer BA). This R34 proposes developmental work on delivering Volunteer BA in senior centers, so as to arrive to a sustainable intervention with standardized procedures. The investigators follow with a small randomized controlled trial (RCT) testing the comparative impact of Volunteer BA versus MSW-provided BA on increased client activity and reduced depressive symptoms.