Acceptance and Commitment Therapy (ACT) is a model for psychology and psychotherapy that stems from behavioural therapy and puts emphasis on values, mindfulness and acceptance processes to promote behavioural change (Hayes, Strosahl, & Wilson, 1999). The aim of this chapter is to introduce a way of working with ACT relevant processes through a psychotherapeutic exercise, adapted to the sport context known as the Sport Lifeline (SLL). Readers will learn how to work with behavioural change in athletic performance using the SLL through case examples from sport practitioners. The Lifeline model was developed as a psychotherapeutic tool in ACT and was originally used in clinical psychology with patients suffering from different forms of psychopathology. It was first presented around a decade ago, and constitutes and combines several components that is central to ACT work (Dahl, Plumb, Stewart, & Lundgren, 2009). We will go through each part of the SLL in this chapter, its underlying theory, how it relates to the different processes of ACT and how each component can be part of promoting behavioural change in athletic performance. The chapter will have an applied focus, and examples from how the SLL was used with an Olympic athlete will be provided. In this way, we hope that readers will understand and learn how to work with ACT relevant processes in the sport context.