Holstein (Northern Low Saxon: Holsteen, Danish: Holsten, Latin and historical English: Holsatia) is the region between the rivers Elbe and Eider. It is part of Schleswig-Holstein, the northernmost state of Germany.

Holstein once existed as the County of Holstein (German: Grafschaft Holstein; 811–1474), the later Duchy of Holstein (German: Herzogtum Holstein; 1474–1866), and was the northernmost territory of the Holy Roman Empire. The history of Holstein is closely intertwined with the history of the Danish Duchy of Schleswig (Danish: Slesvig). The capital of Holstein is Kiel.

Holstein's name comes from the Holcetae, a Saxon tribe mentioned by Adam of Bremen as living on the north bank of the Elbe, to the west of Hamburg. The name means "dwellers in the wood" (Northern Low Saxon: Hol(t)saten; German: Holzsassen).

Formation Date 1474
Dissolution Date 1866
Conflict Name Initiation Year Termination Year Total Killed Total Casuality
First Schleswig War 1848-1850 1848 1850 unknown unknown
Great Northern War 1700-1721 1700 1721 unknown unknown
Count's Feud 1534-1536 1534 1536 unknown unknown