The Constitution of May 3, 1791 (Polish: Konstytucja Trzeciego Maja; Lithuanian: Gegužės trečiosios konstitucija) is generally recognized as Europe's first and the world's second modern codified national constitution. The May 3rd Constitution was instituted as a "Government Act" (Polish: Ustawa rządowa) adopted on that date by the Sejm (parliament) of the Polish-Lithuanian Commonwealth.
The May 3rd Constitution was designed to redress long-standing political defects of the Polish-Lithuanian Commonwealth federation and its traditional system of "Golden Liberty." The Constitution introduced political equality between townspeople and nobility (szlachta) 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 put the sejm at the mercy of any deputy who might choose, or be bribed by an interest or foreign power, to undo legislation passed by that sejm. The Constitution sought to supplant the existing anarchy fostered by some of the country's magnates with a more democratic constitutional monarchy. The document was translated into Lithuanian.
The adoption of the May 3rd Constitution provoked the active hostility of the Commonwealth's neighbors. In the War in Defense of the Constitution, Commonwealth was betrayed by its Prussian ally, Frederick William II, and defeated by Catherine the Great's Imperial Russia allied with the Targowica Confederation, a cabal of Polish magnates who opposed reforms that might weaken their influence. Despite the defeat and the consequent Second Partition of the Polish-Lithuanian Commonwealth, the May 3rd Constitution influenced later democratic movements. It remained, after the demise of the Polish Republic in 1795, over the next 123 years of Polish partitions, a beacon in the struggle to restore Polish sovereignty. In the words of two of its co-authors, Ignacy Potocki and Hugo Kołłątaj, it was "the last will and testament of the expiring Fatherland."