This dissertation has emerged from an involvement in the controversial topic of what constitutes the distinctive character of psychiatric nursing. There is a widespread notion that nursing should be characterised as altruistic actions of care. Do the experiences of patients and nurses reflect this notion of care, and does it represent an appropriate professional self-conception for the individual nurse as well as for nursing as a profession? These questions are at the core of the empirical studies conducted for this dissertation and for the discussion of principles of care. The focus for the collection of empirical material in two locked wards in acute psychiatric departments has been placed on interaction between patients and psychiatric nurses. Participant observation and interviews with patients and nurses were used as research methods. The dissertation consists of six articles that address fundamental principles for nurse-patient interaction. The empirical data show that the nursing practice is full of challenges and that the nurses do not manage to live up to what good psychiatric nursing is supposed to be like. The notion of altruistic care conceals the demanding nature of acute psychiatry; it may, moreover, serve to idealise and camouflage the exercise of power and is liable to afford immunity to criticism. The question arises, whether the altruistic notion of care that prevails in the nursing profession ought to be revised. Mature care is proposed as a possible alternative. Inherent in the concept of mature care is an idea of the importance of the nurses’ balancing their own needs and interests against those of the patients. By also considering the caregiver’s interest, the idea of mature care provides an opportunity to incorporate perspectives of power, including the complex interconnections between power and care. The dissertation argues for the necessity of increasing the space for critical reflection, with a view to developing concepts of care within the profession.