Mountains and Clouds is a sculpture by Alexander Calder located in the Hart Senate Office Building.

The Philip A. Hart Senate Office Building is the third U.S. Senate office building, and is located on 2nd Street NE between Constitution Avenue NE and C Street NE in Washington, D.C., in the United States. Construction began in January 1975, and it was first occupied in November 1982. Rapidly rising construction costs plagued the building, creating several scandals. The structure is named for Philip Hart, who served 18 years as a senator from Michigan. Accessed via a spur of the United States Capitol Subway System, the building features a nine-story atrium dominated by massive artwork, and a large Central Hearing Facility which provides television facilities as well as extensive seating.