This report explores the relationship between subjective wellbeing (SWB) and participation in sport or physical activity among healthy people aged 16 to 25. This relationship is studied by analysing data from four large samples: 1) a UK sample from the British Household Panel Survey and Understanding Society; 2) an English sample from the Active People Survey and the Taking Part survey; 3) a European sample of residents in Berlin, London and Paris from a study conducted at the London School of Economics; and 4) an American sample from the American Time Use Survey. Overall, the analysis reveals positive associations with various measures of SWB. In particular, the young, healthy adults who do sport or physical activity are usually more satisfied with their life, happier on the whole, and also find their life more worthwhile, especially if they exercise on a weekly basis. Moreover, they normally feel happier, less stressed, and a greater sense of purpose during sport or physical activity, compared to how they feel on average during other daily activities. It is further observed, however, that life satisfaction does not vary as people increase or decrease their participation over time, while moving from exercise to other activities during a typical day (and vice versa) is strongly linked to changes in mood. These findings indicate that sport and physical activity have little direct impact on how people feel overall, but they can significantly affect how they feel moment to moment. Implications for sporting policies are delineated.