In the context of the White Book of Physical and Rehabilitation Medicine (PRM) in Europe, this paper deals with the core concepts at the base of the PRM specialty. These are the essential constituents that make PRM a primary medical specialty, different from all the other medical specialties, and PRM physician the primary medical specialist among the rehabilitation professionals. The core concepts that will be discussed in this Section include: - PRM is a person/functioning oriented specialty, and this makes the specialty different from the organ/disease oriented, or treatment/age specific medical specialties. - PRM physicians have medical responsibilities, like all the other medical specialists, but with an additional specificity of making a functional assessment. - Like the other specialists, PRM physicians provide direct treatments, but they also work leading the multi-professional rehabilitation team, that works in a collaborative way with other professionals and medical specialists. - Due to its function oriented approach, PRM has a multimodal approach including a wide variety of treatment tools (frequently provided by other rehabilitation professionals) and manages all persons' morbidities (health conditions), since it focuses on decreasing impairments and activity limitations to allow the best possible participation of patients. - As PRM bases its work on functioning, it has a transversal role to other specialties: it overlaps with several of them, sharing part of their knowledge, but it is also totally independent from all of them, since it is based on a different and transversal body of knowledge. - PRM is focused on the person and neither on the disease nor on the setting; in fact, PRM is not only transversal to specialties, but also to the settings of care, and PRM physicians should know these different realities: persons with disabilities and those with long-term health conditions in fact move inside the national health systems between various facilities to obtain the best possible functioning and participation through an appropriate rehabilitation process.