The intertwinement of Roman (civil) law and canon law in the medieval Europe is commonly designated as “both laws” (ius utrumque). Medieval canon law was a universal law, which emerged from ecclesiastical as well as ancient Roman legal sources and was at its core a product of scholastic ecclesiastical science of canon lawyers as well as papal legislation. The article outlines three centuries of development and the core content of ecclesiastical legal collections in the period of the classical age of canonist science (12th-14th centuries). The period is characterised primarily by the private collection of canon sources Decretum Gratiani (1140), the most extensive medieval official codification - Liber Extra (1234) as well as its additions Liber Sextus (1298), Clementinae (1317) and Extravagantes. The mission of the papal legislation was to upgrade Roman law provisions in the light of Gospel and theological teachings. The law-making activity of the Church, resembling the vocation of Roman praetor, facilitated the reception Roman law in a society governed by the values of Christian morality.