Hildegard Peplau developed the Interpersonal Relations Theory, which focuses on the nurse-patient relationship and its progression through four phases: orientation, identification, exploitation, and resolution. The theory emphasizes understanding interpersonal processes and developing therapeutic relationships. Peplau identified seven nursing roles to illustrate the dynamic character roles in clinical nursing, and her theory provides a framework for assessment, planning, intervention, and evaluation in caring for patients. Research has found the theory useful for educating oncology patients, ensuring understanding, and developing individualized care plans for families.