In The Heart of ACT, renowned acceptance and commitment therapy (ACT) trainer Robyn Walser explores ACT as a process-based therapy incorporating intrapersonal and interpersonal processes, as well as the six core components of psychological flexibility to connect clinicians to the dynamic and relational implementation of ACT. Engaging clinical scenarios, therapeutic insights, and supervision dialogues are offered to help clinicians move beyond their conceptual understanding of ACT principles to master the nuances of the therapeutic relationship at the heart of ACT. Using the tips and strategies in this professional guide, clinicians will learn to develop a flexible, grounded, and client-centered practice.