This article analysis the institution of impediment of ligamen in the first recension of Gratian’s Decretum. Firstly, the author outlines the contemporary doctrine and the historical evolution of the impedimentum ligaminis until the classical period of canon law. Special attention is being given to the first figures of this impediment and the development process of legal terminology. After the presentation of the most recent scholarship concerning the author of the Decretum and his work, tree causae dealing with the impediment of ligamen have been analyzed. Gratian’s understanding of this institution, being based on the copula theory, is an important milestone in the evolution of the institution of impedimentum ligaminis.