The Duchy of Courland and Semigallia is a duchy in the Baltic region that exists from 1561 to 1569 as a vassal state of the Grand Duchy of Lithuania and from 1569 to 1726 the Polish-Lithuanian Commonwealth, incorporated into the Polish-Lithuanian Commonwealth by Sejm in 1726.

On 28 March 1795, it is annexed by the Russian Empire in the Third Partition of Poland.