The objective of the study is to introduce late modern age legal opinions on custom and its place among sources of law in the Hungarian legal system. It focuses especially on the characteristics and functions of custom and clarifies the relationship between custom and the law as such (lex, act) as another source of law. The Hungarian modern age is characterised by a symbiosis between custom and the law and by a related dispute about how they relate to eachother. The authors of the study focused their attention on a dispute over the derogatory function of custom in relation to the law and highlighted the trend of a major effort towards codification and the related growing importance of lex as a source of law. At the same time custom was losing its “folk character” and gradually gained a forensic form (custom formally included as a basis for court decisions). In Hungarian legal history, custom held an irreplaceable position among sources of law in the legal system, and modern age jurisprudence scholars attempted to develop or reformulate the theoretical principles enshrined in the Opus Tripartitum (1514) (J. Szegedi, S. Huszty, E. Kelemen, A. Kövy, P. Szlemenics, I. Frank, etc.).