The consolidation of the study of the power of medieval queens requires new questions to be considered in order to increase our knowledge of their role in the courts of European monarchies during the Middle Ages. The theoretical conceptualization of their role as the king’s wife is the key to understanding their deeds during their husbands’ reigns, but also to appreciating their own selfidentity as queens. This article aims to analyse what marriage meant as an indissoluble link between the spouses and how the significance of that union was affected when it came to defining queenship. By means of an interpretation of biblical texts related to marriage and its importance in Castilian legislative sources, the role played by the queen will be understood as part of the political body of the Monarchy.