Medicine is a branch of health science concerned with maintaining human health and restoring it by treating disease and injury; it is both an area of knowledge, a science of body systems and diseases and their treatment, and the applied practice of that knowledge. The practice of medical care is shared between the medical profession—physicians or doctors—and other groups of professionals, such as nurses or pharmacists (sometimes called allied health professions).

Historically, only members of the medical profession proper have been considered to actually practice medicine in the strictest sense, in contrast to the allied fields of health care professionals. The medical profession is the social and occupational structure of the group of people formally trained and authorized to apply medical knowledge. Many countries and legal jurisdictions have legal limitations on who may practice medicine or the allied medical fields. Medicine is typically seen as composed of various specialized sub-branches, such as pediatrics, gynecology, neurology, dealing with particular body systems, diseases, or areas of health.

Systems of medical and healthcare practices have existed among human societies since at least the dawn of recorded history. These systems have developed in various ways in different cultures and regions. Medicine as understood in the modern period has historically been considered to be the mainstream tradition which developed in the Western world since the early modern age. Many other traditions of medicine and healthcare are still widely practiced throughout the world, most of which are still considered to be separate and distinct from Western medicine, also called biomedicine or the Hippocratic tradition. The most highly developed systems of medicine outside the Western system are the Ayurvedic tradition of India and traditional Chinese medicine. Various non-mainstream traditions of health care have also developed in the Western world distinct from mainstream medicine. The various other systems practiced among various cultures are sometimes practiced alongside or in cooperation with Western medicine, while sometimes being seen as competing traditions. Veterinary medicine is the practice of health care specialized for other animal species.