During the significant period between Late Medieval Times and the end of Early Modern Era the oath was an important tool of communication not only between the town and its lord but also among the members of the municipal community itself. We can say in general that the oath was a kind of bond to the town structures. From the city scribe to the least servant in the city jail, whenever they were taking up their office there was an obligation to swear an oath to the city council and to the community. The paper will focus on how the municipal self-government’s scope of activity gradually expanded and interfered in more and more areas of urban life. How the town became the community of the oath-bearers. The paper will also focus on how the filiation of municipal law (network of legal relations between towns) reflected in the wording of oaths.