Christiansborg Palace (Danish: Christiansborg Slot, pronounced [kʰʁestjænsˈpɒˀ ˈslʌt, kʰʁæs-]) is a palace and government building on the islet of Slotsholmen in central Copenhagen, Denmark. It is the seat of the Danish Parliament (Folketinget), the Danish Prime Minister's Office, and the Supreme Court of Denmark. Also, several parts of the palace are used by the Danish monarch, including the Royal Reception Rooms, the Palace Chapel and the Royal Stables.

The palace is thus home to the three supreme powers: the executive power, the legislative power, and the judicial power. It is the only building in the world that houses all three of a country's branches of government. The name Christiansborg is thus also frequently used as a metonym for the Danish political system, and colloquially it is often referred to as Rigsborgen ('the castle of the realm') or simply Borgen ('the castle').

The present building, the third with this name, is the last in a series of successive castles and palaces constructed on the same site since the erection of the first castle in 1167. Since the early fifteenth century, the various buildings have served as the base of the central administration; until 1794 as the principal residence of the Danish kings and after 1849 as the seat of parliament.

The palace today bears witness to three eras of Danish architecture, as the result of two serious fires. The first fire occurred in 1794 and the second in 1884. The main part of the current palace, finished in 1928, is in the historicist Neo-baroque style. The chapel dates back to 1826 and is in a neoclassical style. The showgrounds were built from 1738 to 1746, in a baroque style.

Christiansborg Palace is owned by the Danish Government, and is run by the Palaces and Properties Agency. Several parts of the palace are open to the public.