This thesis is written as a collection of research papers through which the cognitive and motivational effects of imagery on sports performance were investigated. A number of research methodologies, ranging from a quasi-experimental design to a multiple-baseline across participants design, were employed to explore the effects of imagery. The first section of this thesis explored the cognitive effects of imagery. Specifically, study I examined the effects of different visual imagery perspectives and kinaesthetic imagery on the acquisition and retention of a simple gymnastics routine. External visual imagery was shown to have superior effects over internal visual imagery for this form-based task. A significant interaction was found in the retention phase; however, follow up tests failed to clarify the nature of the interaction. Study 2 and study 3 further investigated the imagery perspective issue by exploring the strength of relationship between external visual imagery and kinaesthetic imagery, and between internal visual imagery and kinaestlictic imagery. Results indicated that when the participant is the object of the image, kinaesthetic imagery has a greater association with external visual imagery than with internal visual imagery. However, because the tasks that participants imaged were essentially form-based, the results may not generalise to other types of tasks. The second section of the thesis examined the motivational effects of imagery. Study 4 employed a multiple-baseline across participants design to establish the effect of a mastery imagery intervention on sport confidence. Consistent with Paivio's (1985) proposals, the results suggested that imagery has a motivational function as the imagery intervention was found to increase confidence. Study 5 further considered the imagery confidence relationship and two factors which may moderate this relationship, that is skill level and sport-type. The results suggest that in team sport players the type of imagery associated with confidence depends on the skill level of the player