Under the 1783 Nassau Family Pact, those territories of the Nassau family in the Holy Roman Empire at the time of the Pact (Luxembourg and Nassau) were bound to use Salic law, which forbade inheritance by the female line. When William III died leaving only his daughter Wilhelmina as an heir, the crown of the Netherlands, not being bound by the Family Pact, passed to Wilhelmina. However, the crown of Luxembourg could not pass to a woman, leaving the House of Orange-Nassau without a male heir. As a result, the throne went to Adolphe, the dispossessed Duke of Nassau and head of the House of Nassau-Weilburg.
At the death of his uncle, Nikolaus-Wilhelm in 1905, Guillaume IV changed the laws of succession and named his daughter as his heir; the only other male, male-line, descendant of the House of Nassau-Weilburg was Guillaume's cousin, Georg Nikolaus, Count of Merenberg, the product of a morganatic marriage. So, in 1907, Guilliame declared the Counts of Merenberg non-dynastic, naming his own eldest daughter Marie-Adélaïde as heir to the throne. She became Luxembourg's first reigning female monarch upon her father's death in 1912, and upon her own abdication in 1919, was succeeded by her younger sister Charlotte, who married Felix of Bourbon-Parma, a prince of the Duchy of Parma. Charlotte's descendants have reigned until the present day under the name Nassau and are also members of the House of Bourbon-Parma.
- Grand Dukes of Luxembourg:
1905-1912: William IV
2000 - : Henri