Pre-Olympic Games predictions commonly include an increase in population-based physical activity in the host city, as often stated in the bid, but the post-Olympic Games effects on physical activity have not been summarised. In this Series paper, we aim to do the following: examine mentions of a physical activity legacy in pre-Olympic bid documentation; analyse existing physical activity surveillance data collected before, during, and after the Olympic Games in hosting areas around the world; and evaluate Google Trends data surrounding the London 2012 Olympic Games as a case study of community interest in the topic of exercise during the time of the Olympic Games. Before 2007, little mention of physical activity was made in pre-Olympic Games documentation, but, after that, most documents had targets for population physical activity or sports participation. The synthesis of available surveillance data indicates that there was no change in the prevalence of physical activity or sports participation, except for the 2008 Summer Olympics in Beijing and the 1998 Winter Olympics in Nagano; although, the increase in participation in Nagano might not be attributable to the Olympic Games since there was no change in participation in winter sports. The Google Trends data showed an acute spike in searches with the term “Olympic” immediately associated with the London Olympic Games period and showed a sustained peri-Olympic increase in searches with the term “exercise”. By themselves, the Olympic Games have not improved population-wide physical activity but might be an important missed public health opportunity. Such a legacy will require strategic planning and partnerships across the International Olympic Committee and the Olympic, sport, and public health agencies and a thorough evaluation framework implemented throughout the pre-Olympic Games and post-Olympic Games period in the host country.