The House of Nassau is a diversified aristocratic dynasty in Europe. It is named after the lordship associated with Nassau Castle, located in present-day Nassau, Rhineland-Palatinate, Germany. With the fall of the Hohenstaufen in the first half of the 13th century royal power within Franconia evaporated and the former stem duchy fragmented into separate independent states. Nassau emerged as one of those independent states as part of the Holy Roman Empire. The lords of Nassau were originally titled "Count of Nassau", subject only to the Emperor, and then elevated to the princely class as "Princely Counts". Early on they divided into two main branches: the elder (Walramian) branch, that gave rise to the German king Adolf, and the younger (Ottonian) branch, that gave rise to the Princes of Orange and the monarchs of the Netherlands.

Idstein is a town of about 25,000 inhabitants in the Rheingau-Taunus-Kreis in the Regierungsbezirk of Darmstadt in Hesse, Germany. Because of its well preserved historical Altstadt it is part of the Deutsche Fachwerkstraße, connecting towns with fine fachwerk buildings and houses. In 2002, the town hosted the 42nd Hessentag state festival.