In the context of the White Book of Physical and Rehabilitation Medicine (PRM) in Europe, this paper deals with the fundamentals of PRM from a physiological perspective, looking at the human mechanisms both physical and behavioral which are at the base of PRM physicians' work. After a discussion on the development and evolution of PRM that leads to its unique and specific approach, the mechanisms considered include: - repairing processes (and potential of recovery evaluation): repairing processes are mainly related to the quantity and natural history of diseases and impairments, while potential of recovery is also linked to the individual and environmental factors; PRM physicians work on impairments to favor healing or recovery, and propose rehabilitation if there is a potential of recovery: this is related to the prognostic role of PRM physicians; - learning processes: PRM is the specialty of teaching new physical ways and behavioral approaches to make patients participate at best through improvement of impairments and modification of activities; in this perspective, during repair and rehabilitation processes, PRM physicians and the rehabilitation team are teachers of new motor and behavioral strategies; - compensatory processes (adaptation/habilitation/rehabilitation): PRM physicians teach patients how to adapt to the new (acquired) health condition using compensatory mechanisms based on other body structures/functions, behavioral changes and/or assistive devices (or technical aids) (prosthesis and orthosis); during growth PRM physicians aim at allowing a complete (and compensatory) development of the intact function, not to be impaired by the original disease; compensatory processes are related to activities; - management skills: PRM physicians are managers of people and resources; they manage patients and their caregivers, to teach and allow them to reach the best possible participation, also focusing on maintenance; they lead the team, with the aim to make it function at best for the sake of the patient; finally, they manage resource allocation for the functioning of patients and team; - communication skills: PRM physicians need to develop very good communication skills, so to teach, inform and educate patients and their caregivers: this will allow the proper behavioural changes and also the correct physical compensations.