The Great Sejm, also known as the Four-Year Sejm (Polish: respectively, Sejm Wielki or Sejm Czteroletni; Lithuanian: Didysis seimas or Ketverių metų seimas) was a Sejm (parliament) of the Polish-Lithuanian Commonwealth that was held in Warsaw between 1788 and 1792. Its principal aim became to restore sovereignty to, and reform, the Commonwealth politically and economically.
The Sejm's great achievement was the adoption of the Constitution of May 3, 1791, often described as Europe's first modern written national constitution, and the world's second, after the United States Constitution. The Polish Constitution was designed to redress long-standing political defects of the federative Polish-Lithuanian Commonwealth and its system of Golden Liberties. The Constitution introduced political equality between townspeople and nobility and placed the peasants under the protection of the government, thus mitigating the worst abuses of serfdom. The Constitution abolished pernicious parliamentary institutions such as the liberum veto, which at one time had placed a sejm at the mercy of any deputy who might choose, or be bribed by an interest or foreign power, to undo all the legislation that had been passed by that sejm. The May 3rd Constitution sought to supplant the existing anarchy fostered by some of the country's reactionary magnates, with a more egalitarian and democratic constitutional monarchy.
The reforms instituted by the Great Sejm and the Constitution of May 3, 1791, were undone by the Targowica Confederation and the intervention of the Russian Empire at the invitation of the Targowica Confederates.