Little is known about older adults' perceptions of organized programs that support exercise behavior. We conducted semi-structured interviews with 39 older adults residing in King County, Washington, who either declined to join, joined and participated, or joined and then quit a physical activity-oriented program. We sought to explore motivators and barriers to physical activity program participation and to elicit suggestions for marketing strategies to optimize participation. Two programs supporting exercise behavior and targeting older persons were the source of study participants: Enhance(®)Fitness and Physical Activity for a Lifetime of Success. We analyzed interview data using standard qualitative methods. We examined variations in themes by category of program participant (joiner, decliner, quitter) as well as by program and by race. Interview participants were mostly females in their early 70s. Approximately half were non-White, and about half had graduated from college. The most frequently cited personal factors motivating program participation were enjoying being with others while exercising and desiring a routine that promoted accountability. The most frequent environmental motivators were marketing materials, encouragement from a trusted person, lack of program fees, and the location of the program. The most common barriers to participation were already getting enough exercise, not being motivated or ready, and having poor health. Marketing messages focused on both personal benefits (feeling better, social opportunity, enjoyability) and desirable program features (tailored to individual needs), and marketing mechanisms ranged from traditional written materials to highly personalized approaches. These results suggest that organized programs tend to appeal to those who are more socially inclined and seek accountability. Certain program features also influence participation. Thoughtful marketing that involves a variety of messages and mechanisms is essential to successful program recruitment and continued attendance.