The influence of implicit cognitive processes on social behaviour has been heavily scrutinised in recent years. A burgeoning body of literature now indicates that implicit processes are particularly predictive of those behaviours that are spontaneously performed and difficult to control. Although interest in implicit cognition has been strong in many fields, few studies have investigated the role of implicit cognitive processes on physical activity. In this article we highlight the avenues through which implicit processes might influence different forms of activity. Two of the most prominent theories in sport and exercise psychology – the theory of planned behaviour and self-determination theory – are used as templates through which discussion is focused. Studies on implicit processes that have utilised these theories are reviewed and critiqued, and the implications of findings from these studies on the prediction of physical activity are discussed. The final section includes a discussion of recent theorising on the mechanisms through which implicit cognitive processes might change. It is hoped that discussion of these important issues will stimulate research into the role of implicit cognitive processes in physical activity.