This review examines program features that influence attendance and adherence to group-based physical activity (PA) by older adults. Medline, PubMed, CINAHL plus, PsycINFO, and the Cochrane Library were searched for studies published from 1995–2016. Quantitative and qualitative studies investigating factors related to PA group attendance or adherence by persons aged 55 years and over were included. Searching yielded eight quantitative and 13 qualitative studies, from 2,044 titles. Quantitative findings identified social factors, instructor characteristics, PA types, class duration and frequency, and perceived PA outcomes as important for attendance and adherence, whilst qualitative studies identified settings, leadership, PA types, observable benefits, and social support factors. Studies were predominantly low- to moderate-quality. This review identified design and delivery considerations for group-based PA programs to inform best-practice frameworks and industry capacity building. Future research should use longitudinal and mixed-methods designs to strengthen evidence about facilitators of program reach and engagement.