The szlachta was a privileged class with origins in the Kingdom of Poland. It gained considerable institutional privileges during the 1333-1370 reign of Casimir the Great. In 1413, following a series of tentative personal unions between the Grand Duchy of Lithuania and the Kingdom of Poland, the existing Lithuanian nobility formally joined the class. As the Polish-Lithuanian Commonwealth (1569–1795) evolved, its membership grew to include leaders of Ducal Prussia and the Ruthenian lands.
The origins of the szlachta are unclear and have been the subject of a variety of theories. Traditionally, its members were owners of landed property, often in the form of folwarks. The nobility negotiated substantial and increasing political privileges for itself until the late 18th century.
During the Partitions of the Polish-Lithuanian Commonwealth from 1772 to 1795, its members lost their privileges. Until 1918, the legal status of the nobility was then dependent on policies of the Russian Empire, the Kingdom of Prussia, and the Habsburg Monarchy. Its privileges were legally abolished in the Second Polish Republic by the March Constitution in 1921.