In most countries, only persons with a medical license bestowed either by a specified government-approved professional association or a government agency are authorized to practice medicine. Licenses are not granted automatically to all people with medical degrees. A medical school graduate must receive a license to practice medicine before he or she can be called a physician in a legal sense, a process that usually entails testing or examinations by a medical board. The medical license is the documentation of authority to practice medicine within a certain locality.

In the United States, medical licenses are usually granted by individual states. Only those with medical degrees from schools listed in the AVICENNA Directory for medicine or the FAIMER International Medical Education Directory are permitted to apply for medical licensure.

The federal government does not grant licenses. A physician practicing in a federal facility may have a license from any state, not just the one they are residing in. The practice of "tele-medicine" has made it common for doctors to consult or interpret images and information from a distant location. Most states have special licensure for this.