In the last decade, interest in the impact of the built environment on physical activity has grown. Policies and community and neighbourhood infrastructure provide opportunities to be active, and facilitate incidental physical activity, such as walking for transport or use of stairs. Theoretical ecological models provide a basis for physical activity research and practice, focussing attention on multiple levels of influence on behaviour (i.e., individual, social-environmental and physical environmental). However, few studies have quantified the relative contribution of these correlates on behaviour, leaving policy-makers and practitioners wondering about where to target their efforts: people or places? This paper draws on theory, evidence to date and case studies to argue that comprehensive interventions targeting both people and places are required to increase physical activity. The joint influence of place and people is discussed in the context of data showing that the likelihood of walking at recommended levels is nearly eight times higher (OR 7.84; 95% CI 4.41-13.91) in people with both a supportive environment and positive cognitions compared with those low on both. To increase physical activity requires multi-sector partnerships and comprehensive long-term multi-pronged interventions that include short-, medium- and long-term strategies aimed at bringing about cultural shifts favouring physical activity over sedentary alternatives, and the creation of a supportive built environment. The health sector can contribute by implementing public education programs, workforce development, building the evidence-base and advocating for change. However, to improve policies and infrastructure in places the commitment of sectors outside of health is critical.