The Indian Health Service (IHS) is an operating division (OPDIV) within the U.S. Department of Health and Human Services (HHS). IHS is responsible for providing direct medical and public health services to members of federally recognized Native American Tribes including American Indian and Alaska Native people. IHS is the principal federal health care provider and health advocate for Native people in the United States.

The IHS provides health care in 37 states to approximately 2.2 million out of 3.7 million American Indians and Alaska Natives (AI/AN). As of April 2017, the IHS consisted of 26 hospitals, 59 health centers, and 32 health stations. Thirty-three urban Indian health projects supplement these facilities with various health and referral services. Several tribes are actively involved in IHS program implementation. Many tribes also operate their health systems independent of IHS. It also provides support to students pursuing medical education to staff Indian health programs.

"The provision of health services to members of federally recognized tribes grew out of the special government-to-government relationship between the federal government and Indian tribes. This relationship, established in 1787, is based on Article I, Section 8 of the Constitution, and has been given form and substance by numerous treaties, laws, Supreme Court decisions, and Executive Orders."

Health services for American Indian and Alaska Natives in the United States were first assigned to the Department of War in 1803 and later the Office of Indian Affairs in 1824. With the creation of the Division of Indian Health in 1924, field nurses were hired and Public Health Service officers filled positions to address staffing shortages. Policy changes as a result of the Meriam Report (1928) led to funding and the first preventive medicine program. While resources increased in the 1930s, both staffing and funding declined with the start of World War II. Calls to improve health, sanitation, and facilities continued after the war as Indian termination policy shaped postwar debate.

Following the Indian Health Facilities Act (Transfer Act) of 1954, the IHS was established in 1955, transferring departmental authority to the Public Health Service. At the same time, former surgeon general Thomas Parran published a report which detailed health problems among Alaska Natives. The IHS's report to Congress in 1957 (known as the "Gold Book" for the color of its cover) and the Parran Report presented the first comprehensive study of health conditions and recommendations based on the findings. There were four priorities or functions identified:

to assemble a competent health staff; establish adequate facilities where services could be provided; institute extensive curative treatment for the seriously ill; and develop a full-scale prevention program that would reduce the excessive amount of illness and early deaths, especially for preventable diseases.

IHS employs approximately 2,650 nurses, 700 physicians, 700 pharmacists, 100 physician assistants, and 300 dentists, as well as a variety of other health professionals such as nutritionists, registered medical-record administrators, therapists, community health representative aides, child health specialists, and environmental engineers and sanitarians. It is one of two federal agencies mandated to use Indian Preference in hiring. This law requires the agency to give preference to qualified Indian applicants before considering non-Indian candidates for employment, although exceptions apply.

IHS draws a large number of its professional employees from the U.S. Public Health Service Commissioned Corps. This is a non-armed service branch of the uniformed services of the United States. Professional categories of IHS Commissioned corps officers include physicians, physician assistants, nurses, dentists, therapists, pharmacists, engineers, environmental health officers, and dietitians.