Reception of Roman law, which, in the High Middle Ages hit the legal environment of almost the entire Europe, had also imminently influenced the development of law in the Czech lands. Aside from Canon law, which often used Roman law terms in documents, the issue of reception of Roman law in the Czech lands was closely connected mainly with the medieval cities which, thanks to their market-economy nature, were very close to the economic and social structure of Ancient Rome. There were many Czech towns that followed Roman law as a secondary source of law and the Moravian Royal city of Brno was one of them. In 1380s, a general manual on law was written in the Brno's town office. The manual was intended for the needs of the Czech towns and villages and its title was Manipulus vel directorium iuris civilis (Manual of Town Law). It was written by the town's public notary John of Gelnhausen, who had practice in Brno. Writing this manuscript, the author drew inspiration from the Roman law codification Corpus iuris civilis, particularly from the 16th and 17th title of the fiftieth book of Digest, which outlines rules of interpretation and legal definitions. The Gelnhausen's work is unique, as no other legal book of that period which had been written in the Czech lands contained such a vast corpus of interpretation rules and principles. Thus, the goal of this article is to present an analysis of some of the rules of interpretation from the Manual of Town Law which John of Gelnhausen borrowed from Digest. An emphasis will be put especially on the rules of interpretation concerning juridical acts. The authors of this paper are going to focus not only on the essence of these rules, but they will also try to outline the importance of these rules for the period legal practice.