Betty Neuman's Systems Model provides a comprehensive holistic and system-based approach to nursing that contains an element of flexibility. The theory focuses on the response of the patient system to actual or potential environmental stressors and the use of primary, secondary, and tertiary nursing prevention intervention for retention, attainment, and maintenance of patient system wellness.

The basic assumptions of the model are:

Each patient system is a unique composite of factors and characteristics within a range of responses contained in a basic structure. Many known, unknown, and universal stressors exist. Each differ in their potential for upsetting a client's usual stability level. Each patient has evolved a normal range of responses to the environment referred to as the normal line of defense. It can be used as a standard by which to measure health deviation. The particular inter-relationships of patient variables can, at any point in time, affect the degree to which a client is protected by the flexible line of defense against possible reaction to stressors. When the flexible line of defense is incapable of protecting the patient against an environmental stressor, that stressor breaks through the line of defense. The client is a dynamic composite of the inter-relationships of the variables, whether in a state of illness or wellness. Wellness is on a continuum of available energy to support the system in a state of stability. Each patient has implicit internal resistance factors known as LOR, which function to stabilize and realign the patient to the usual state of wellness. Primary prevention is applied in patient assessment and intervention, in identification and reduction of possible or actual risk factors. Secondary prevention relates to symptomatology following a reaction to stressors, appropriate ranking of intervention priorities, and treatment to reduce their noxious effects. Tertiary prevention relates to adjustive processes taking place as reconstitution begins, and maintenance factors move them back in a cycle toward primary prevention. The patient is in dynamic, constant energy exchange with the environment.

The major concepts of Neuman's theory are content, which is the variables of the person in interaction with the environment; basic structure or central core; degree to reaction; entropy, which is a process of energy depletion and disorganization moving the client toward illness; flexible line of defense; normal line of defense; line of resistance; input-output; negentropy, which is a process of energy conservation that increases organization and complexity, moving the system toward stability or a higher degree of wellness; open system; prevention as intervention; reconstitution; stability; stressors; wellness/illness; and prevention.

In the Systems Model, prevention is the primary intervention. It focuses on keeping stressors and the stress response from having a detrimental effect on the body. Primary prevention occurs before the patient reacts to a stressor. It includes health promotion and maintaining wellness. Secondary prevention occurs after the patient reacts to a stressor and is provided in terms of the existing system. It focuses on preventing damage to the central core by strengthening the internal lines of resistance and removing the stressor. Tertiary prevention occurs after the patient has been treated through secondary prevention strategies. It offers support to the patient and tries to add energy to the patient or reduce energy needed to facilitate reconstitution.

In the Neuman's theory, a human being is a total person as a client system and the person is a layered, multidimensional being. Each layer consists of a five-person variable or subsystem. The subsystems are physiological, which refers to the physiochemical structure and function of the body; psychological, which refers to mental processes and emotions; socio-cultural, which refers to relationships, and social/cultural expectations and activities; spiritual, which refers to the influence of spiritual beliefs; and developmental, which refers to those processes related to development over the lifespan.

Neuman explains environment as the totality of the internal and external forces which surround a person, and with which they interact at any given time. These forces include the intrapersonal, interpersonal, and extra-personal stressors, which can affect the person's normal line of defense and so can affect the stability of the system. The environment has three components: the internal, which exists within the client system; the external, which exists outside the client system; and the created, which is an environment that is created and developed unconsciously by the client, and is symbolic of system wholeness.

The Systems Model of health is equated with wellness, and defined as "the condition in which all parts and subparts, or variables, are in harmony with the whole of the client." The client system moves toward illness and death when more energy is needed than what's available. The client system moves toward wellness when more energy is available than is needed.

Neuman views nursing as a unique profession concerned with the variables that influence the response the patient might have to a stressor. Nursing also addresses the whole person, giving the theory a holistic perspective. The model defines nursing as "actions which assists individuals, families and groups to maintain a maximum level of wellness, and the primary aim is stability of the patient-client system, through nursing interventions to reduce stressors." Neuman also says the nurse's perception must be assessed in addition to the patient's, since the nurse's perception will influence the care plan he or she sets up for the patient. The Systems Model views the role of nursing in terms of the degree of reaction to stressors, as well as the use of primary, secondary, and tertiary interventions.

In Neuman's Systems Model nursing process, there are six steps, each with specific categories of data about the patient.

First is the assessment of the patient, which looks at: actual and potential stressors; condition and strength of basic factors and energy sources; characteristics of flexible and normal lines of defense, lines of resistance, degree of reaction and potential for reconstitution; interaction between the patient and his or her environment; life process and coping factors for optimal wellness; and the perceptual difference between the care giver and the patient.

Second, the nurse makes a diagnosis by interpreting the data collected. The data includes health-seeking behaviors, activity intolerance, ineffective coping, and ineffective thermoregulation. The third step in the nursing process is to set goals. The ultimate goal is to keep the client system stable. From the goals, a plan is created, which focuses on strengthening lines of defense and resistance. That plan is implemented using primary, secondary, and tertiary preventions. Finally, the nursing process is evaluated to determine whether or not balance was restored, and a stable state maintained.