Despite the significant increase in years that an individual can now expect to live in the 21st century, there is growing evidence that the price for greater longevity may be worsening health due to the higher prevalence of nonfatal but disabling conditions. This sobering news suggests the need for expanded scientific inquiry directed at understanding the multilevel factors that promote or prevent physical activity (PA) participation and the adoption of healthy lifestyle behaviors and the types of intervention strategies that will be most effective in positively changing behavior at different life stages. Fruitful areas of future scientific inquiry include exploring other types and intensities of PA aimed at increasing PA participation while reducing sedentary behavior, better understanding the role of the physical and social environment in promoting PA participation, and designing and evaluating multilevel PA interventions that are better tailored to the activity preferences, goals, and expectations of a diverse older adult population, and flexibly delivered in real-world settings. Finally, conducting research aimed at better differentiating normal age-associated changes from those that are disease-related will be fundamental to reversing the negative stereotypes that currently shape the public’s view of the aging process.