Knowledge is limited with regard to the progress of the nurse and patient through the phases of the psychiatric nurse-patient relationship (PNPR). Relationship progress is indicative of patient progress in the healing and recovery process. Hildegard Peplau described the phases of the therapeutic relationship in her Interpersonal Relations Theory (IRT). This review of literature describes the state of nursing science using IRT as the theoretical framework. Research conducted on the progress of the PNPR has generated evidence of the relevance of IRT to clinical practice, the importance of the PNPR to the patients themselves, and the importance of nursing knowledge regarding the progress of the orientation phase of the PNPR to patient care. However, all studies were done in Canada, and additional studies are needed. Knowledge of the relationship established between psychiatric nurses and patients is essential to the nursing process in psychiatric mental health settings.