Claudius Ptolemy composed his Geography in the city of Alexandria, one of the most prominent intellectual centres of the Roman Empire. His work offers a comprehensive description of the known world as well as insight into the practice of scholarly geography during the second century CE. Ptolemy’s most important innovation in this field was his use of geographical coordinates to create maps of the world, and his catalogue, with its latitudes and longitudes of thousands of localities, is one of our most valuable sources on the antique oikoumenē. Very little is known, however, about the sources and working methods that Ptolemy employed to produce his Geography. This book focuses on Ptolemy’s description of the Iberian peninsula and examines two problematic and interlinked topics relating to the origins of the catalogue of localities: Ptolemy’s sources and scientific methods on the one hand, and the textual transmission of the Geography, from Ptolemy to the extant manuscripts, on the other.