In this chapter we draw on our applied experiences and research to highlight how perfectionistic athletes can be supported using Acceptance and Commitment Therapy (ACT). The first part of the chapter describes ACT and research that has examined its use for perfectionism. In keeping with other chapters in this section of the book, the second part of the chapter presents a case example of a perfectionistic athlete. Our case example is an aspiring young athlete who in making the transition to the senior performance squad has begun to experience emotional and behavioural problems. Our novel contribution to previous work of this kind is our focus on ACT. Few studies have adopted ACT interventions to reduce perfectionism even though we believe it to be a valuable way of doing so. In addition, there are even fewer exemplars of how to implement this type of intervention in sport. As such, our intention is that the chapter serves as a guide for practitioners unfamiliar with ACT and is a useful addition to other illustrative examples of how to work effectively with perfectionistic athletes.