Arnstein (German: [ˈaʁnʃtaɪn] ⓘ) is a town in the Main-Spessart district in the Regierungsbezirk of Lower Franconia (Unterfranken) in Bavaria, Germany.

Arnstein's Stadtteile are: Town rights were granted in 1333 by Emperor Louis the Bavarian.

The noun Aar can follow the weak declension, in which case the genitive form is Aaren.

The “Sunhouses” were built collaboratively by the 20 builders in the framework of the promotional programme for experimental home building, thereby reducing acquisition and planning costs.

It marks the spot where the 50th parallel of north latitude crosses the 10th meridian of east longitude: 50°N 10°E / 50°N 10°E / 50; 10.