Roy's model of nursing sees an individual as a set of interrelated systems, biological, psychological, and social. The individual tries to maintain a balance between each of these systems and the outside world. However, there is no absolute level of balance. According to Roy we all strive to live within a band where we can cope adequately. This band will be unique to an individual. The adaptation level is the range of adaptability within which the individual can deal effectively with new experiences.
Callista Roy maintains there are four main adaptation systems which she calls modes of adaptation. She calls these the 1. the physiological - physical system 2. the self-concept group identity system 3. the role mastery/function system 4. the interdependency system.