A three-phase study will be used to refine and implement an established theory-based culturally relevant physical activity promotion intervention for obese African American women. Phase 1 (Aim 1a) will include formative research where 25 African American women provide feedback (via 9 focus groups) to further refine the physical activity intervention by specifying the deep structure cultural relevance of the theoretical mediators of self-regulation, self-efficacy, social support, behavioral capability, and outcome expectations.5 Phase 2 will focus on technical development of the refined culturally tailored intervention and 1-month demonstration trial of the Smartphone-delivered physical activity promotion program. Phase 3 (Aims 1b and 1c) will test the intervention and delivery strategy in a two-arm randomized trial where 60 sedentary, obese African American women will receive either the 8-month culturally relevant smartphone-delivered physical activity intervention or a 8-month wellness contact control condition