Peplau published her Theory of Interpersonal Relations in 1952, and in 1968, interpersonal techniques became the crux of psychiatric nursing. The Theory of Interpersonal Relations is a middle-range descriptive classification theory. It was influenced by Henry Stack Sullivan, Percival Symonds, Abraham Maslow, and Neal Elger Miller.

The four components of the theory are: person, which is a developing organism that tries to reduce anxiety caused by needs; environment, which consists of existing forces outside of the person, and put in the context of culture; health, which is a word symbol that implies forward movement of personality and other other human processes toward creative, constructive, productive, personal, and community living.

The nursing model identifies four sequential phases in the interpersonal relationship: orientation, identification, exploitation, and resolution.

The orientation phase defines the problem. It starts when the nurse meets the patient, and the two are strangers. After defining the problem, the orientation phase identifies the type of service needed by the patient. The patient seeks assistance, tells the nurse what he or she needs, asks questions, and shares preconceptions and expectations based on past experiences. Essentially, the orientation phase is the nurse's assessment of the patient's health and situation.

The identification phase includes the selection of the appropriate assistance by a professional. In this phase, the patient begins to feel as if he or she belongs, and feels capable of dealing with the problem which decreases the feeling of helplessness and hopelessness. The identification phase is the development of a nursing care plan based on the patient's situation and goals.

The exploitation phase uses professional assistance for problem-solving alternatives. The advantages of the professional services used are based on the needs and interests of the patients. In the exploitation phase, the patient feels like an integral part of the helping environment, and may make minor requests or use attention-getting techniques. When communicating with the patient, the nurse should use interview techniques to explore, understand, and adequately deal with the underlying problem. The nurse must also be aware of the various phases of communication since the patient's independence is likely to fluctuate. The nurse should help the patient exploit all avenues of help as progress is made toward the final phase. This phase is the implementation of the nursing plan, taking actions toward meeting the goals set in the identification phase.

The final phase is the resolution phase. It is the termination of the professional relationship since the patient's needs have been met through the collaboration of patient and nurse. They must sever their relationship and dissolve any ties between them. This can be difficult for both if psychological dependence still exists. The patient drifts away from the nurse and breaks the bond between them. A healthier emotional balance is achieved and both become mature individuals. This is the evaluation of the nursing process. The nurse and patient evaluate the situation based on the goals set and whether or not they were met.

The goal of psychodynamic nursing is to help understand one's own behavior, help others identify felt difficulties, and apply principles of human relations to the problems that come up at all experience levels. Peplau explains that nursing is therapeutic because it is a healing art, assisting a patient who is sick or in need of health care. It is also an interpersonal process because of the interaction between two or more individuals who have a common goal. The nurse and patient work together so both become mature and knowledgeable in the care process.

The nurse has a variety of roles in Hildegard Peplau's nursing theory. The six main roles are: stranger, teacher, resource person, counselor, surrogate, and leader.

As a stranger, the nurse receives the patient in the same way the patient meets a stranger in other life situations. The nurse should create an environment that builds trust. As a teacher, the nurse imparts knowledge in reference to the needs or interests of the patient. In this way, the nurse is also a resource person, providing specific information needed by the patient that helps the patient understand a problem or situation. The nurse's role as a counselor helps the patient understand and integrate the meaning of current life situations, as well as provide guidance and encouragement in order to make changes. As a surrogate, the nurse helps the patient clarify the domains of dependence, interdependence, and independence, and acts as an advocate for the patient. As a leader, the nurse helps the patient take on maximum responsibility for meeting his or her treatment goals. Additional roles of a nurse include technical expert, consultant, tutor, socializing and safety agent, environment manager, mediator, administrator, record observer, and researcher.

Some limitations of Peplau's theory include the lack of emphasis on health promotion and maintenance; that intra-family dynamics, personal space considerations, and community social service resources are less considered; it can't be used on a patient who is unable to express a need; and some areas are not specific enough to generate a hypothesis.