This monograph is an epigraphic study of the Roman auxiliary units raised on the Iberian Peninsula based on a corpus of over 750 inscriptions. It presents the literary and epigraphic evidence for late Republican allied and auxiliary forces and for the structure of imperial auxiliary units. It then examines the recruiting practices of the auxilia, the settlement of veterans, and the evidence for the personal relationships of the soldiers enlisted in these units as they are recorded in the epigraphic record, including inscriptions on stone and military diplomas.