Mercantile courts (known as mercanzie, merchants’ chambers, domus mercatorum, consulates, etc.) are receiving increasing attention from scholars. They can be investigated on the political-institutional and economic level as well as on the institutional and legal level. The continuous intertwining of these interpretative paths contributes to making the history of mercantile courts a topic of extreme interest. The aim of this study is to investigate the functioning of the Officium Mercancie of Genoa through the continuous dialogue between daily practice and legislation. It is divided into two sections: the first is dedicated to the reconstruction of administrative competences, the second to the daily practice of the court.