This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book focuses on emotional pain and its transformation in psychotherapy from the theoretical framework represented by emotion-focused therapy. It provides a unique framework that builds on the model of emotional transformation first presented by Pascual-Leone and Greenberg. The emotion transformation model is used as a framework, organising a theory of psychopathology and theory of psychotherapy. Emotion-focused therapy is a research-informed psychological therapy that to date has mainly been studied in the context of depression, trauma, and couple distress. The book presents a theory of human suffering and a model of therapy that addresses that suffering. The model of suffering assumes that the experienced emotional pain is a response to an injury that prevents or violates the fulfilment of the basic human needs of being loved, safe and acknowledged.