Orne is a department in the northwest of France, named after the Orne River. Orne is among the 83 departments formed following the French Revolution, on 4th March, 1790. It was formed from parts of the ex-provinces of Normandy and Perche. Orne is in the district of Basse-Normandie neighbouring Eure, Eure-et-Loir, Sarthe, Mayenne, and Calvados. It is the only department of Basse Normandie and Haute Normandie to be closed in. The residents of the department are called Ornais.

Orne is one of the three departments of the Lower Normandy region, the other ones being Manche and Calvados. It is situated in the south of the region, hence has borders with the two other departments, and also with Mayenne, Sarthe, Eure et Loir et Eure. It is the merely Norman section not to have a seafront. The department of Orne, as most of departments in France, was unnaturally created following the Revolution. The maximum point in the department is situated in the forest of Ecouves north of Alengon, reaches 1368 ft.