A hospital corpsman (HM) or corpsman (/ˈkɔːrmən/ CORE-man) is an enlisted medical specialist of the United States Navy, who may also serve in a U.S. Marine Corps unit. The corresponding rating within the United States Coast Guard is Health Services Technician (HS). The U.S. Navy Hospital Corps was created on 17 June 1898, with hospital corpsman used as a generic name for the applicable personnel while various other official names (including hospital apprentice, hospital steward, pharmacist's mate) were used for the rating; after World War II, hospital corpsman became the official name for the rating.

Hospital corpsmen work in a wide variety of capacities and locations, including shore establishments such as naval hospitals and clinics, aboard ships, and as the primary medical caregivers for sailors while underway. Hospital corpsmen are frequently the only medical care-giver available in many fleet or Marine units on extended deployment. In addition, hospital corpsmen perform duties as assistants in the prevention and treatment of disease and injury and assist health care professionals in providing medical care to sailors and their families.

They may function as clinical or specialty technicians, medical administrative personnel and health care providers at medical treatment facilities. They also serve as battlefield corpsmen with the Marine Corps, rendering emergency medical treatment to include initial treatment in a combat environment. Qualified hospital corpsmen may be assigned the responsibility of independent duty aboard ships and submarines, Fleet Marine Force, SEAL and Seabee units, and at isolated duty stations where no medical officer is available.

Hospital corpsmen were previously trained at Naval Hospital Corps School, Great Lakes, Illinois, and the U.S. Naval Hospital Corps School San Diego, California, until the 2011 Base Realignment and Closure Bill caused Hospital Corps School to be relocated to the Medical Education and Training Campus (METC) at Joint Base San Antonio, Texas. Naval Hospital Corps School was also located at NRMC Balboa in San Diego, California.

During the Vietnam War, many of the 16-week Naval Hospital Corps school graduates went directly to 8404 Field Medical Service School (FMSS) at Camp Lejeune, North Carolina, or Camp Pendleton, California, for nine weeks of field training, before deployment to a Marine Corps unit in South Vietnam.

In the United States Marine Corps, the colloquial form of address for a Hospital Corpsman who rate to wear the Navy's Fleet Marine Force (FMF) warfare device (showing they were or are attached to an FMF Unit) is "Doc", which is generally used as a sign of respect. Hospital Corpsman who are not authorized to wear the device would still be referred to by their rate and rank.

Prior to the establishment of the hospital corps in 1898, enlisted medical support in the U.S. Navy was limited in scope. In the Continental Navy and the early U.S. Navy, medical assistants were assigned at random out of the ship's company. Their primary duties were to keep the irons hot and buckets of sand at the ready for the operating area. It was commonplace during battle for the surgeons to conduct amputations and irons were used to close lacerations and wounds. Sand was used to keep the surgeon from slipping on the bloody ship deck. Previously, corpsmen were commonly referred to as loblolly boys, a term borrowed from the Royal Navy, and a reference to the daily ration of porridge fed to the sick. The nickname was in common use for so many years that it was finally officially recognized by the Navy Regulations of 1814. In coming decades, the title of the enlisted medical assistant would change several times—from loblolly boy, to nurse (1861), and finally to bayman (1876). A senior enlisted medical rating, surgeon's steward, was introduced in 1841 and remained through the Civil War. Following the war, the title surgeon's steward was abolished in favor of apothecary, a position requiring completion of a course in pharmacy.

Still, there existed pressure to reform the enlisted component of the Navy's medical department—medicine as a science was advancing rapidly, foreign navies had begun training medically skilled sailors, and the U.S. Army had established an enlisted hospital corps in 1887. Navy Surgeon General J.R. Tryon and subordinate physicians lobbied the Navy administration to take action. With the Spanish–American War looming, Congress passed a bill authorizing establishment of the U.S. Navy Hospital Corps, signed into law by President William McKinley on 17 June 1898. Three ratings were created therein—hospital apprentice, hospital apprentice first class (a petty officer third class), and hospital steward, which was a chief petty officer.