Single-session therapy (SST) is a collaborative, direct, and transparent approach to providing treatment that emphasizes service users having active and empowered roles in determining the focus, solutions, and extent of the therapy. Clinicians developed SST as many adult mental health service users only receive a single session of therapy. Service users tend to be satisfied with SST and often chose to not return for additional sessions. SST emphasizes the strengths, resources, and resilience of service users and increases treatment access while limiting costs. Some of the impetus for SST is based on research indicating that rapid improvement tends to occur early in treatment with additional sessions being less impactful. In Part I, I provide a descriptive overview and synthesis of the SST literature. I conclude Part I by naming assumptions of long-term therapy and SST. In Part II, I describe approaches to conducting SST, apply SST to music therapy, and provide a critical reflection of SST.