Physical activity is important to maintain a healthy lifestyle. Levels of physical activity decrease across the lifespan, and findings suggest only between 13-32% of University students are physically active at the recommended level. Research has found that ca. 50% of motivated individuals fail to enact on their intentions to be physically active. The theory of planned behaviour (TPB) was described, limitations and additions identified and its use outlined in three areas of investigation predicting physical activity: motivation, volition and intervention. Method: Student Activity and Lifestyle Study at Aberdeen (SALSA), a web-based survey, invited all students at the University of Aberdeen to respond to three questionnaires across the 2005/06 and 2006/07 academic years. SALSA received responses from 1418 and 1273 participants at the start of each academic year, respectively. Social cognitions (e.g. intention, perceived control), self-reported physical activity levels and attendance to the University’s sport facilities were measured. A double-blind randomised controlled trial investigated the efficacy two planning interventions, delivered via the internet, aiming to increase PA. Results and Summary: Findings suggest that students who are motivated benefit from making plans when, where and how to take part in physical activity, and plan how to cope with potential barriers and obstacles. Participants who are more certain of their intentions, aware of effort, the standards required and monitor themselves are more likely to be physically active, even though they are equally motivated and perceive themselves to be in control. Participant who were active in the past were more likely to attend the University’s sport facilities. However, the planning interventions did not increase students’ activity levels or attendance to the University’s sport facilities. Adherence to intervention protocol was low (between 58.8% to 76.7%) and participants dropping out of SALSA were large across both academic years.