Indian Health Service's mission is to provide health care and related services for American Indian and Alaska Natives, as well as their descendants. The organization delivers health care, social, and environmental health services for nearly 2 million members of more than 560 tribes. Most live in 35 states, primarily in the western US and Alaska. The organization's health service delivery system includes 30 hospitals, some 65 health centers, about 30 health stations, and 35 Urban Indian health projects. IHS also offers mental health and substance abuse programs as well as dental health services. The agency is part of the US Department of Health and Human Services and operates on a budget of about $4.3 billion.