Reciprocal Guarantee of Two Nations

The Reciprocal Guarantee of Two Nations (Polish: Zaręczenie Wzajemne Obojga Narodów), also Reciprocal Warranty of Two Nations, Mutual Pledge of the Two Nations (Lithuanian: Abiejų Tautų tarpusavio įžadas) and Mutual Assurance of the Two Nations, was an addendum, adopted on 20 October 1791 by the Great Sejm, to the Polish-Lithuanian Constitution of 3 May 1791. In the preamble of this guarantee the dualistic form of the state was confirmed and it had equal status to the Union of Lublin (1569).

The Mutual Assurance of the Two Nations stated implementing principles that had not been spelled out in the Constitution. The document specified the nature of the Polish–Lithuanian union and affirmed "the unity and indivisibility", within a single state, of the Crown of the Kingdom of Poland and the Grand Duchy of Lithuania.

Statutes and Constitutions of Lithuania
Part of a series on the politics and government of Lithuania

Neminem captivabimus acts, 1430 Casimir's Code, 1468 The First Statute, 1529 The Second Statute, 1566 Henrician Articles, 1573 The Third Statute, 1588 Constitution of 3 May 1791 Mutual Pledge of the Two Nations, 1791 Temporary Constitutions of 1918-1920 Constitution of 1922 Klaipėda Convention, 1924 Constitution of 1928 Constitution of 1938 Lithuanian SSR Constitution of 1940 Partisans Declaration of 1949 Lithuanian SSR Constitution of 1978 Temporary Basic Law of 1990 Current Constitution, 1992