This chapter provides a brief overview of the theories and their relations to state and trait anxiety as well as competitive anxiety, perfectionism and eating disorders or disordered eating. It discusses practical implications for coaches in youth sports. Self-determination theory as a macro-theory of human motivation as well as achievement goal theory are both widely used frameworks for studying motivational processes in the sport and exercise domain. Deci and Ryan differentiate various types of motivation which can be located on a continuum of self-determination. The basic assumption of achievement goal theory is that in achievement situations individuals seek to develop or demonstrate competence and avoid failure based on incompetence. There are two dimensions of the perceived motivational climates; these are called the task-involving climate and the ego-involving climate. The 2 × 2 achievement goal framework of achievement goals distinguish between ego/performance-approach goals, ego/performance-avoidance goals, task/mastery-approach goals and task/mastery-avoidance goals. Perfectionism is a common and prevalent characteristic in high-level athletes.