This research has investigated the effects of different types of imagery on motor skill learning and sport performance, using quantitative and qualitative methodologies. The first section of this thesis examined the effects of different visual imagery perspectives on the learning and performance of a slalom-type task and a gymnastic-type task. The use of an external visual perspective was found to enhance the speed of completion of the slalom-type task, and also enhance the recall of the gymnastic-type task. In contrast, internal visual imagery enhanced the accuracy of performance on the slalom-type task. However, no significant differences between high-level slalom canoeists and high-level artistic gymnasts in their ability to form visual imagery from different perspectives, suggested that athletes from both sports use both perspectives. The second section of the thesis employed a qualitative methodology in order to study the uses of imagery by high level slalom canoeists and artistic gymnasts. Consistent with Paivio (1985), it was found that imagery was used for both cognitive and motivational functions in both competitive and training environments. The nature of the sport was also reported to influence image content. The third section of the thesis examined the use of imagery by gymnasts to enhance emotion and motivation, using an Interacting Cognitive Subsystems framework. High levels of exercise-induced arousal without imagery were found to depress mood, motivation and efficacy expectations, however, imagery use stabilised these effects. The results of this research programme suggest that imagery is used by sport performers in a variety of ways to enhance learning and performance. Qualitative and quantitative evidence was found to suggest that the efficacy of imagery is dependent on the ability of the image to supply the athlete with information which is most appropriate for the purpose of the imagery.