Medicine is the art, science, and practice of caring for a patient and managing the diagnosis, prognosis, prevention, treatment or palliation of their injury or disease. Medicine encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness. Contemporary medicine applies biomedical sciences, biomedical research, genetics, and medical technology to diagnose, treat, and prevent injury and disease, typically through pharmaceuticals or surgery, but also through therapies as diverse as psychotherapy, external splints and traction, medical devices, biologics, and ionizing radiation, amongst others.

Medicine has been practiced since prehistoric times, during most of which it was an art (an area of skill and knowledge) frequently having connections to the religious and philosophical beliefs of local culture. For example, a medicine man would apply herbs and say prayers for healing, or an ancient philosopher and physician would apply bloodletting according to the theories of humorism. In recent centuries, since the advent of modern science, most medicine has become a combination of art and science (both basic and applied, under the umbrella of medical science). While stitching technique for sutures is an art learned through practice, the knowledge of what happens at the cellular and molecular level in the tissues being stitched arises through science.

Prescientific forms of medicine are now known as traditional medicine and folk medicine. They remain commonly used with, or instead of, scientific medicine and are thus called alternative medicine. As an example, evidence on the effectiveness of acupuncture is "variable and inconsistent" for any condition, but is generally safe when done by an appropriately trained practitioner. In contrast, alternative treatments outside the bounds not just of scientific medicine, but also that of safety and efficacy are termed quackery. This can encompass an array of practices and practitioners, irrespective of whether they are prescientific (traditional medicine and folk medicine) or modern pseudo-scientific, including chiropractic which rejects modern scientific germ theory of disease (instead believing without evidence that human diseases are caused by invisible subluxation of the bones, predominantly of the spine and less so of other bones), with just over half of chiropractors also rejecting the science of immunization.