Casimir ensured stability and great prospects for the future of the country. He established the Corona Regni Poloniae – the Crown of the Polish Kingdom, which certified the existence of the Polish lands independently from the monarch. Prior to that, the lands were only the property of the Piast dynasty.

At the Sejm in Wiślica, on 11 March 1347, Casimir introduced reforms to the Polish judicial system and sanctioned civil and criminal codes for Great and Lesser Poland, earning the title "the Polish Justinian".