Town above the valley of the upper Nahe in Rheinland-Pfalz in western Germany, near the border with the Saarland. It is the capital of the Landkreis of Idar-Oberstein.
The town was part of the County of Sponheim, and, after its partition in 1223, of Hintere Sponheim. In 1437, after the death of the last Count, it became the joint property of the Margrave of Baden and the Count of Veldenz (who was succeeded on his death in 1444 by his son-in-law, the Count Palatine of Simmern and Zweibrücken).
In 1584, with the consent of the Margrave of Baden-Baden, Karl, the youngest son of the Count Palatine of Zweibrücken, became the ruler of Birkenfeld. Karl’s heir acquired Bischweiler in Alsace in 1630 and it became the seat of a junior line, which also acquired Rappoltstein in Alsace about the same time as it inherited Birkenfeld from the senior line in 1671. The Count Palatine of Birkenfeld succeeded as Duke of Zweibrücken in 1731. Birkenfeld passed to Baden in 1776 when the Duke and the Margrave of Baden agreed to divide the Sponheim lands, . It was occupied by France in the 1790s and annexed in 1797, becoming part of the Department of the Sarre.
Under the terms of the Treaty of Vienna in 1815, Oldenburg (in the north-west of the German Confederation) was to receive a part of the Department of the Sarre, and in 1817, Peter, the Regent of Oldenburg for his insane cousin, became Prince of Birkenfeld. Birkenfeld remained an enclave of Oldenburg within the Rheinprovinz of Prussia until 1937 when it was merged into that province. In 1947 it became part of the new Land of Rheinland-Pfalz.