This paper explores physical activity adherence among older adults in clinical research. We address the unique challenges associated with promoting physical activity, including the amount of time and effort, perceived benefits, and recommendations from professionals. We explore useful strategies to enhance adherence in the realm of physical activity interventions, including the development of theory-based physical activity interventions that acknowledge participant needs and expectations, promote self-regulatory skills, view exercise as an ongoing process subject to relapse, and utilize phone contacts for home-based activity programs. We conclude with directions for future clinical trials to enhance exercise adherence that include the need for a precise definition and operationalization of adherence, linkages between physical activity interventions and theory, and the study of exercise in both structured and home-based settings. Control Clin Trials 2000;21:212S-217S