The pedigree of judicial institutions in Poland goes back far back into tribal times. This paper is an attempt to synthetically outline the institutions of the justice system in Poland during the feudal period and during the Piast Monarchy. The development of judicial institutions that developed in The Kingdom of Poland will be presented, taking into account the specific social and political system for the formation of their practice, organization and system principles. It is in the institutions and practice of The Piast Dynasty Poland and then of the Noble Republic that we should look for from the origins of the concepts and judicial institutions that we know these days. The article discusses the formation of courts in the tribal and ancestral times, i.e. before the formal establishment of the Polish State and in the Piast period, which were the beginning of the Polish judiciary. The activity of King Casimir the Great is particularly important, as he initiated full legislative activity, which later became the foundation of the judiciary of the First Republic period.