Ostholstein (German pronunciation: [ˈɔsthɔlʃtaɪn] ⓘ; Danish: Østholsten) is a district in Schleswig-Holstein, Germany.

It is bounded by (from the southwest and clockwise) the districts of Stormarn, Segeberg and Plön, the Baltic Sea and the city of Lübeck.

Geographically, the district covers the vast majority of what is considered to be the peninsular of Wagria.

Holsatian Switzerland is an area full of lakes and woody hills, which is shared with the adjoining district of Plön.

The coat of arms displays: Media related to Kreis Ostholstein at Wikimedia Commons