Lotharingia is a medieval successor kingdom of the Carolingian Empire, comprising the Low Countries, the western Rhineland, the lands today on the border between France and Germany, and what is now western Switzerland.

It is born of the tripartite division in 855, of the kingdom of Middle Francia, itself formed of the threefold division of the Carolingian Empire by the Treaty of Verdun in 843.

Neither Lotharingia nor Middle Francia have any natural coherence, but each is conceived as a territorial division of a larger realm.

In 870, Lotharingia, after a brief interregnum, is divided by the Treaty of Meerssen between its neighbors, East Francia and West Francia.

After brief wars in 876 and 879 West Francia cedes its half of Lotharingia to East Francia by the Treaty of Ribemont (880).

The Lotharingian aristocracy, in attempting to assert its right to elect a sovereign, joins the other East Frankish lands in deposing their king, Charles the Fat, in 887.

Under a series of dukes that begins under the child king Louis IV in 903, the Lotharingians frequently swap allegiance between the East and West Frankish kings.

In 939, the East Frankish king Otto I roings the reigning duke Gilbert to heel and incorporates Lotharingia into his realm as one of the "younger" stem duchies, whose dukes have a vote in royal elections.

While the other stem duchies are tribal or national identities, Lotharingia's identity is solely political.In 959, the Lotharingian duke Bruno the Great divides the duchy between Lotharingia superior (Upper Lorraine) and Lotharingia inferior (Lower Lorraine), giving each to the rule of a margrave.

Except for one brief period (1033–44, under Gothelo I), the division is never reversed and the margraves soon raise their separate fiefs into dukedoms.

In the twelfth century the ducal authority in Lower Lorraine becomes fragmented, causing the formation of the Duchy of Limburg and the Duchy of Brabant, whose rulers retain the title Duke of Lothier (derived from "Lotharingia").

With the disappearance of a "lower" Lorraine, the duchy of Upper Lorraine becomes the primary referent for "Lorraine" within the Holy Roman Empire.

After centuries of French invasions and occupations, Lorraine is finally ceded to France at the close of the War of the Polish Succession (1737).

In 1766 the duchy is inherited by the French crown and becomes the province of Lorraine.

In 1871, after the Franco-Prussian War, the German-speaking part of Lorraine is merged with Alsace to become the province of Alsace-Lorraine in the German Empire.

Today the greater part of the French side of the Franco-German border belongs to the Lorraine région.