The Treaty of Hadiach (Polish: ugoda hadziacka; Ukrainian: гадяцький договір) was a treaty signed on 16 September 1658 in Hadiach (Hadziacz, Hadiacz, Гадяч) between representatives of the Polish–Lithuanian Commonwealth (represented by S. Bieniewski and K. Jewłaszewski) and Ukrainian Cossacks (represented by Hetman Ivan Vyhovsky and starshina Yuri Nemyrych, architect of the treaty, and Pavlo Teteria). It was designed to elevate the Cossacks and Ruthenians to the position equal to that of Poland and Lithuania in the Polish–Lithuanian union and in fact transforming the Polish–Lithuanian Commonwealth into a Polish–Lithuanian–Ruthenian Commonwealth (Rzeczpospolita Trojga Narodów, "Commonwealth of Three Nations").