The purposes of this review are to (1) describe recruitment and retention strategies for physical activity interventions focusing on underserved populations and (2) identify successful strategies which show the most promise for "best practices" recommendations to guide future research. The method used was systematic review. Data on recruitment and retention strategies were abstracted and analyzed according to participant characteristics, types of strategies used, and effectiveness using an ecological framework. Thirty-eight studies were identified. Populations included African American (n=25), Hispanic (n=8), or Asian (n=3) groups. Successful recruitment strategies consisted of partnering with respected community stakeholders and organizations, well-trained study staff ethnically, linguistically, and culturally matched to the population of interest, and use of multiple advertising channels. Successful retention strategies included efficient administrative tracking of participants, persistence, skillful teamwork, and demonstrating a positive, caring attitude towards participants. Promising recruitment and retention strategies correspond to all levels of ecological influence: individual, interpersonal, organizational, and societal.