Hildegard E. Peplau has had a major influence on nursing since she wrote the first comprehensive, theoretically informed nursing theory after Florence Nightingale’s. Peplau’s perspective was psychodynamic and her theoretical writing has influenced almost every area of nursing practice. In this article I introduce the life and work of Peplau, taking Peplau’s classic Interpersonal Relationships in Nursing as my point of departure. Moreover, I discuss some of the later developments of the theory. I criticize Peplau’s theoretical position and evaluate it in the light of present day nursing practice.