The human-environment interaction model is a modification of the Neuman systems model and is a macro systems approach designed to provide an organizing framework to understand the client's relationship with the environment and to intervene appropriately through preventive, corrective, and rehabilitative measures. It assists in organizing phenomena and shows relationships of various components. The structural elements of the model include context, process, and substantive categories. The substantive parts include theoretical concepts, operational definitions, and a mental-visual picture that permits the theoretical concepts to be readily perceived and understood. The major categories are the physiologic, psychologic, sociocultural, and developmental (PPSD) variables. These are defined and applied as they relate to the health of clients. The model incorporates and illustrates the collaborative decision-making process encompassing three levels of prevention. Together, these provide a framework for action to promote, maintain, and restore the health of individuals, families, aggregates, and the community.