Included here are brief outlines of the careers of forty-eight magnates who held comital rank in the twelfth-century kingdoms of Leon and Castile. The constraints upon space have meant that they are far from being comprehensive biographies. Among the most notable omissions, no reference is made to the military campaigns in which these nobles participated, to the periods of time that they spent at court, nor to the subsequent careers of each and every one of their offspring. Nevertheless, it is my hope that this list will prove a useful source of information for those who wish to find out more about some of the most illustrious members of twelfth-century lay society. The list includes not only those grandees who were indigenous to León and Castile, but also those outsiders who successfully integrated themselves into the Leonese-Castilian power structure: the Catalans Armengol VI and Armengol VII of Urgel, Ponce de Cabrera and Ponce de Minerva, and the Portuguese Velasco Sánchez. On the other hand, some counts have been deliberately excluded from the list. First, the Frenchmen Raymond of Burgundy (d. 1107) and his cousin Henry (d. 1112) who married into the royal house of León in the late eleventh century and whose careers have in any case already been the object of important scholarly study. Second, those counts who, like Nuño Velázquez, Sancho Pérez and Sancho Sánchez, disappear from the record very soon after 1100, or who, as in the case of Alvaro and Gonzalo Núñez de Lara, did not obtain comital rank until after 1200.