The flag of Schleswig-Holstein is a horizontal tricolour of blue, white, and red.
The flag was introduced in 1843 and banned in 1845. It was reintroduced in 1867 after the Prussian conquest of Schleswig-Holstein. It was again abolished 1935.
After the British Military Government made Schleswig-Holstein a German state in 1946, this flag was first hoisted after some debate on August 29, 1946. It was formally established as the flag on January 18, 1957. The plain tricolour is the state's civil flag. Government authorities use the state flag (Landesdienstflagge), where the flag is defaced by the state coat of arms.
The tricolour was previously used for the Prussian province of Schleswig-Holstein (1868-1946).