Arnold I of Laurenburg

Arnold I of Laurenburg (died ca. 1148), an early member of the House of Nassau, was from 1123 co-Count of Laurenburg. The House of Nassau would become an important aristocratic family in Germany, from which are descended the present-day Kings of the Netherlands and Grand Dukes of Luxembourg.

Arnold was the second son of Count Dudo-Henry of Laurenburg (German: Dudo-Heinrich von Laurenburg) and Anastasia of Arnstein, daughter of Count Louis II of Arnstein. Count Dudo, considered the founder of the House of Nassau, had already built the castle of Laurenburg around 1080, and laid the foundations of Nassau Castle in present day Nassau, Germany, around 1100. After 1120, Arnold ruled from Nassau Castle together with his brother Robert I.

In 1124, Arnold became the Vogt of Idstein. Idstein had come under the control of Count Dudo in 1122. Arnold also later became the Vogt of St. George's Monastery Church in Limburg an der Lahn.

The name of Arnold's wife is unknown. He had two, and perhaps, children:

• Henry (Heinrich) I, co-Count of Nassau, 1160 - August 1167
• Robert (Ruprecht) III, "the Bellicose", co-Count of Nassau, 1158–1191
• (possibly) Gerhard, Count of Laurenburg, 1148

• Gerhard more likely was the son of Arnold I's brother, Robert I. See explanation under Robert I of Nassau.