The paper examines the process of the unification of substantive and procedural criminal law in the Yugoslav state during the interwar period. Despite its unitary and centralistic administrative organization, the Yugoslav state at the time was characterized by legal particularism. Among the territories that encompassed the Kingdom of Serbs, Croats, and Slovenes there were substantially different legal systems, and hence, considerably diverse sources of law, since they had been parts of different political and territorial units prior to the unification. After the unification, there were six criminal codes and equally as many codes of criminal procedure in force in the territory of the Kingdom. Reformation and unification of substantive and procedural criminal law became an inevitable task, which was regarded as being urgent because achieving the standardization of the legal system was considered as a step forward, which would facilitate and solidify the unity and the proclaimed centralism that the state sought. Despite the initial efforts towards unification of criminal law that were begun by the beginning of 1919, the process was nevertheless turbulent, slow-going, and inefficient. Such circumstances were deeply conditioned by the permanent political instability, which emerged from continuous changes in the person of the Minister of Justice that always occurred in very short periods. The unification of criminal law was finally achieved only after the proclamation of the Dictatorship in 1929.