The Orne (French: [ɔʁn] ⓘ) is a river in Grand Est, north-eastern France, which is a left tributary of the Moselle and sub-tributary of the Rhine.

Eure), or onna (a river)[citation needed] as mentioned in Endlicher's glossary of Gallic names De nominibus Gallicis, in which these words are translated into Latin as flumen.

It flows through Étain, Conflans-en-Jarnisy, Auboué, Homécourt, Jœuf, Moyeuvre-Grande, Rosselange, Rombas, Clouange, Vitry-sur-Orne, Gandrange and Richemont, where it joins the Moselle at an elevation of 155 metres (509 ft).

The section of about 2 kilometres (1.2 mi) from Joeuf to the naval base at Homècourt is marked by a number of bridges and footbridges permitting passage from one bank to the other.

The Orne is a substantial river, similar to its neighbours in the West Lorraine region which rise in the Côtes de Meuse.

The Orne's flow rate has been measured over a period of 40 years (1967–2007) at Rosselange, in the Moselle department a short way upstream of the confluence.

The Orne exhibits strongly marked seasonal fluctuations, such as are very often found in the east of France, with high water in winter/spring bringing the monthly average up to between 20.2 and 26.9 cubic metres per second (710 and 950 cu ft/s) from December to March inclusive, with a maximum in February.