The important role that the environment plays in health and well-being is widely accepted, as is the impact that the built and natural environment can have on levels of physical activity. As levels of physical activity are a key determinant of health, promoting physical activity through actions to improve the environment is a priority for public health action. The challenge for public health is to ensure that the way the environment is shaped and transformed by a range of professionals, organisations and agencies, maximises health gain in relation to health, including physical activity. This article discusses how the public health profession can and should contribute to generating and disseminating evidence to inform decision-making processes for designing environments to promote physical activity. There are significant challenges to building and applying the evidence base in this area. These include the complex environments in which interventions operate, disciplinary differences in approaches to evidence generation and use, and the fact that public health has little responsibility for environmental change. However, case studies of best practice, presented in the article, offer a snapshot of how challenges can be overcome, to build an accessible evidence base and help to improve the environment for the promotion of physical activity.