This thesis examined the relationships of the conceptions of sport ability, achievement goals, and intrinsic motivation in Physical Education. Studies 1 and 2 investigated the psychometric properties of the Conceptions of the Nature of Athletic Ability Questionnaire (CNAAQ), a measure of sport ability beliefs. In addition, the relationships between ability beliefs, goal orientations, perceived competence, and behavioural indicators (intentions and amotivation) were also examined. Study 3 examined the interrelationships between ability beliefs, achievement goals, perceived competence, behavioural regulation, and amotivation using cluster analysis. Study 4 experimentally manipulated sport ability beliefs and examined their causal influence on achievement goals and motivation patterns when faced with failure. Study 5 examined the effects of goal involvement on enjoyment and intrinsic motivation under positive feedback. Taken all together, this thesis has made significant contributions to the area of motivation in sport and exercise domain.