Growth of  Parliament and privileges for the nobility 

By ancient custom the kings of Poland convened general assemblies called sejm, attended by legati terrestres, representatives of the noble or equestrian (knights') estate. By the late 15th century under King Jan I Olbracht (Ioannes Albertus, John Albert) a national assembly had emerged consisting of King, Senate (or Royal Council), and the House of the legati terrestres regionally elected in public assemblies  (sejmiki), and a few representatives for the richest cities. It was one of the oldest European parliaments.
As of the reign of Louis of Hungary and the Koszyce Privileges of 1374, kings of Poland solicited the support of the politically and economically ascendant nobility by granting privileges, especially tax exemptions and the famous Neminem Captivabimus Nisi Jure Victum (We Shall Not Imprison Anyone Unless He Be Proved Guilty by the Law) statute of 1432, which predated the English Habeas Corpus Act by 256 years. These privileges gradually curtailed the monarch's prerogatives, culminating in the Nihil Novi statute (1505), which prevented the King from making any important decisions without the approval of Sejm.