The House of Nassau-Weilburg, a branch of the House of Nassau, ruled a division of the County of Nassau, which was a state in what is now Germany, then part of the Holy Roman Empire, from 1344 to 1806.

On 17 July 1806, upon the dissolution of the Holy Roman Empire, the principalities of Nassau-Usingen and Nassau-Weilburg both joined the Confederation of the Rhine.

Under pressure from Napoleon, both principalities merged to become the Duchy of Nassau on 30 August 1806, under the joint rule of Prince Frederick August of Nassau-Usingen and his younger cousin, Prince Frederick William of Nassau-Weilburg.

However, Frederick William died from a fall on the stairs at Schloss Weilburg on 9 January 1816 and it was his son William who later became duke of a unified Nassau.

The first two Grand Dukes of Luxembourg, Adolphe and Guillaume IV, were Protestants, however, the Christian denomination of the house changed after Grand Duke Guillaume IV's marriage to Marie Anne de Braganza, who was Catholic.