There is strong evidence that older adults greatly benefit from regular physical activity. Yet, older age is consistently associated with lower levels of aerobic physical activity and strength training and higher levels of sedentary behavior, underscoring the need to better understand physical activity behavior in this population. Reviews of interventions to increase physical activity have overall yielded promising results. Interventions based on behavior theory appear to be more effective than non-theory-based interventions, yet strategies from these theories are underutilized in both research and practice. This paper discusses the importance of behavioral interventions, cites findings from the Active for Life initiative to illustrate several key concepts, and provides recommendations to address significant gaps in the literature, including the use of theory, mediation analyses, physical activity maintenance, diversity of participants, and dissemination and translational research.