Elite athletes have to contend with potential conflicts between the demands of their sport and other aspects of their lives. However, the impact of such conflicts has been under-investigated. This thesis adopts concepts from organisational research into life domain conflicts and applies them to elite sport. The thesis comprises a general introduction, four empirical chapters, and a general discussion. The main goals were to: extend life-sport conflicts research by developing sound measures for both directions of conflict (i.e., life to sport and sport to life); examine a self-determination theory-based model where life-sport conflicts are conceptualised as social contexts that influence motivation towards sport, and how perfectionism moderates this relationship; and explore prospectively whether life domain conflicts and perfectionism predict the extent to which international athletes’ remain within the elite level of sport across a two year period. Advanced statistical procedures (e.g., Bayesian structural equation modelling) are deployed to rigorously achieve these goals. Findings from the studies provide evidence that: life-sport conflicts and sport-life conflicts can be problematic for elite athletes; life domain conflicts are bi-directional and distinct, so only by examining conflicts in both directions can they be adequately represented; life-sport conflicts can be conceptualised as antecedents to self-determined motivation; adaptive perfectionism can attenuate, whereas maladaptive perfectionism can amplify the negative motivational impact of life-sport conflicts; and that sport-free time conflict, a combination of family-sport conflict and adaptive perfectionism, and maladaptive perfectionism prospectively predict international standing at two years. The focus of the thesis is innovative, being the first research to demonstrate that conflicts between life domains exist in elite sports. It contributes to motivation research by showing that life-sport conflicts are negatively associated with self-determined motivation. Findings also highlight that perfectionism plays an important role in the relationship between life-sport conflicts and athlete motivation and maintaining elite performance levels.