This research examined the role of motivational cognitions and belief systems in the process of exercise adoption and maintenance. Deci and Ryan (1985,1990) outline a continuum of behavioural regulation that ranges from non-self-determined regulation (external regulation) to completely self-determined regulation (intrinsic regulation). Prochaska and DiClemente (1984) describe five stages of behaviour change that range from no thoughts of changing (precontemplation) to maintenance of change (maintenance). They also outline ten strategies and techniques for encouraging and maintaining change which are known as the processes of change. Kelly (1955,1963) presents a personal construct theory which maintains that each of us has theories or constructs about people and events which guide beliefs and behaviour. Research, which integrated these concepts, was conducted in three phases. A Behavioural Regulation in Exercise Questionnaire was developed in the first phase of research. Results from the second phase of research revealed that regulation of exercise behaviour was more self-determined in the later than in the earlier stages of change. This highlights the importance of motivational considerations in understanding the change process. Only five of the ten processes of change made a meaningful contribution to differentiation among the stages in females while only three of the processes made a meaningful contribution to differentiation among the stages in males. These processes showed moderate to strong correlations with those forms of behavioural regulation that are at least somewhat selfdetermined. In addition, those successfully changing their stage of exercise behaviour over a three month period increased their use of the counter-conditioning process. However, confirmatory factor analysis of the Processes of Change for Exercise Questionnaire brought into question the factorial validity of the measure. The final phase of research examined personal construction of exercise as a function of stage of change and self determination for exercise. Those in the maintenance stage of change had strong opinions about and strong preferences for certain modes of exercise, while references to being too serious about exercise were strongest in the preparation and precontemplation stages. The preparation stage was marked by desire for more motivation and push to take more exercise. As self-determination decreased references to lack of time for exercise and a desire to have more motivation or put in more effort increased. This research suggests that conflict between desired self (more active and healthy) and actual self (not the fit and active type) may be greatest in the preparation and action stages of change where the act of exercising is still low in self-determination and not yet reconciled with one's sense of self