The collection ‘Legislation of the Seym of the 16th–18th C.’ has been expanded with 156 items resulting from the digitization of the edition of 'Volumina Constitutionum' prepared by Stanisław Grodziski, Wacław Uruszczak, and Irena Dwornicka, Volume 2, Book 1, covering the years 1550–1585. This volume contains texts of key importance for the political system and law of the Kingdom of Poland, the Grand Duchy of Lithuania, and the Polish-Lithuanian Commonwealth, including, among others, the records of the enforcement Sejm sessions of the 1560s , the Sejm of Lublin in 1569, at which the Polish-Lithuanian Union was crowned, and the legislative output of the Sejm sessions during the first two interregna, when the constitutional foundations of the First Polish-Lithuanian Commonwealth were established. The digitization was carried out thanks to financial support provided from the funds of the Heritage Priority Research Area as part of the Strategic Program Initiative of Excellence at the Jagiellonian University (ID.UJ), in cooperation with the Księgarnia Akademicka Publishing House.