Schleswig-Holstein (pronounced [ˈʃleːsvɪç ˈhɔlʃtaɪn] ( listen)) is the northernmost of the sixteen states of Germany, comprising most of the historical duchy of Holstein and the southern part of the former Duchy of Schleswig. Its capital city is Kiel; other notable cities are Lübeck, Flensburg and Neumünster.

The former English name was Sleswick-Holsatia, the Danish name is Slesvig-Holsten, the Low German name is Sleswig-Holsteen, the Dutch name is Sleeswijk-Holstein and the North Frisian name is Slaswik-Holstiinj. Historically, the name can also refer to a larger region, containing both present-day Schleswig-Holstein and the former South Jutland County (Northern Schleswig) in Denmark.

The term "Holstein" derives from Old Saxon, Holseta Land, meaning "the land of those who dwell in the wood" (Holz and Holt mean wood in modern Standardised German and in literary English respectively). Originally, it referred to the central of the three Saxon tribes north of the Elbe river, Tedmarsgoi, Holcetae, and Sturmarii. The area of the Holcetae was between the Stör river and Hamburg, and after Christianization their main church was in Schenefeld. Saxon Holstein became a part of the Holy Roman Empire after Charlemagne's Saxon campaigns in the late eighth century. Since 811 the northern frontier of Holstein (and thus the Empire) was marked by the river Eider.