Federal lands are lands in the United States owned by the federal government. Pursuant to the Property Clause of the United States Constitution (Article 4, section 3, clause 2), Congress has the power to retain, buy, sell, and regulate federal lands, such as by limiting cattle grazing on them. These powers have been recognized in a long line of United States Supreme Court decisions.

The only mention in the United States Constitution of the specific types of land the federal government is authorized to own outside Washington D.C., in Article 1, Section 8, refers to "Places purchased by the Consent of the Legislature of the State in which the same shall be, for the erection of Forts, Magazines, Arsenals, Dock-yards, and other needful Buildings."

The federal government owns about 640 million acres (2.6 million km²) of land in the United States, about 28% of the total land area of 2.27 billion acres (9.2 million km²). The majority of federal lands (610.1 million acres (2.469 million km²) or 95 percent area in 2015) are administered by the Bureau of Land Management (BLM), United States Fish and Wildlife Service (FWS), National Park Service (NPS), or United States Forest Service (USFS). BLM, FWS, and NPS are part of the United States Department of the Interior, while the Forest Service is part of the United States Department of Agriculture. An additional 11.4 million acres (46 thousand km²) of land (about 2% of all federal land) is owned by the United States Department of Defense (DOD). The majority of federal lands are located in Alaska and the Western states.