The therapeutic relationship is a concept that has become central to the identity and practice of mental health nurses since it was formulated by nursing theorists in the 1930s. Most commonly associated with the work of the late Hildegard Peplau, the therapeutic relationship has been considered both fundamental to nursing generally and to capture the unique focus of mental health nursing: interpersonal engagement with consumers of mental health services. However this dual role, and the absorption of specialist mental health nursing education into generalist nursing education, has left the specialty in a problematic situation in identifying and articulating its unique contribution to mental health care. This problem is at its most acute in inpatient settings where, ironically, mental health nursing has its strongest historical roots. In this study I have sought to describe mental health nurses' perceptions of the therapeutic relationship. Rather than ask, as many previous studies have done, whether mental health nurses interact therapeutically with consumers I have sought the views of mental health nurses themselves. A constructionist research paradigm has been used to develop the research. From within a constructionist paradigm, phenomena are seen as socially constructed rather than objectively available for observation. Language is regarded not as a transparent medium of description, but as theory-laden. Focus groups were used to gather data from experienced nurses in three different practice settings; inpatient care, community care and from nurse-therapists. By attending to the group as the focus of analysis it was possible to develop a broad view of the therapeutic relationship. The themes reported here describe the therapeutic relationship as fundamental to mental health nursing, independent of theoretical accounts of mental health nursing and mental health care, and with a wide scope, from facilitative listening to involvement in coercive interventions. The therapeutic relationship in mental health nursing has emerged as a phenomenon socially constructed by its development as part of a therapeutic discourse in mental health care in the middle of the last century, and through the influence of current practice contexts. From the description developed in this study it has been possible to make recommendations for mental health nursing education, research and practice.