A physician or medical doctor is a professional who practices medicine, which is concerned with promoting, maintaining, or restoring human health through the study, diagnosis, and treatment of disease, injury, and other physical and mental impairments. Physicians may focus their practice on certain disease categories, types of patients, or methods of treatment—known as specialist medical practitioners—or assume responsibility for the provision of continuing and comprehensive medical care to individuals, families, and communities—known as general practitioners. Medical practice properly requires both a detailed knowledge of the academic disciplines (such as anatomy and physiology) underlying diseases and their treatment—the science of medicine—and also a decent competence in its applied practice—the art or craft of medicine. Both the role of the physician and the meaning of the word itself vary around the world. Degrees and other qualifications vary widely, but there are some common elements, such as medical ethics requiring that physicians show consideration, compassion, and benevolence for their patients.