Specific Aims: This application proposes to randomize community-dwelling, older adults to one of two, 12-week activity interventions that target either increased moderate-to-vigorous physical activity (MVPA) or decreased sedentary behavior (SED). The primary aim of this research is to evaluate the effect of a behavioral intervention targeting decreased SED vs. increased MVPA on objectively monitored activity (minutes of SED and MVPA). The secondary aim is to evaluate the effect of the SED intervention vs. the MVPA intervention on functional and psychosocial outcomes. To the investigators knowledge, this research will provide unique experimental evidence that SED can be altered in an older adult population and will yield key pilot data on the expected effect size for an intervention targeting SED vs. MVPA.