The royal House of Nassau is one of the most prominent dynasties in Europe. It is named after the German town of Nassau, which is located in the Rhineland-Palatinate. The first person to be called Count of Nassau was Heinrich I, who lived in the first half of the 13th century. His sons Walram and Otto split the Nassau possessions. The descendants of Walram became known as the Walram Line, which became important in the Nassau county. The descendants of Otto became known as the Otton Line, which inherited parts of the Nassau county, France and the Netherlands.


The House of Orange-Nassau stem from the Otton Line. The second person was Engelbert I, who offered his services to the Duke of Burgundy, married a Dutch noblewoman and inherited lands in the Netherlands, with the barony of Breda as the core of the Dutch possessions.

The importance of the Nassaus grew throughout the 15th and 16th century. Hendrik III of Nassau-Breda was appointed stadtholder of Holland, Zeeland and Utrecht by Charles of Ghent in the beginning of the 16th century. Henry was succeded by René of Châlon-Orange in 1538, who was, as his full name stated, Prince of Orange. When René died prematurely on the battlefield in 1544 his possessions passed to his nephew, William I of Orange. From then on the family members called themselves "Orange-Nassau."


The House of Nassau-Weilburg became rulers of Luxembourg.