This book highlights the profound change in the nature of geography between the late eighteenth century and the mid-twentieth century. Those who called themselves geographers in the 1760s were almost exclusively concerned with how to describe the world and its intellectual foundations. In the eighteenth century, geographical publications represented what could be seen and measured, and they were characterised above all by universal geographies, manuals of field surveying and cartography, and maps drawn by comparison with written or graphic sources. But the debate over the size and shape of the earth, between Cassini and Newton’s followers, showed the limits of representation. The transition to more modern concerns was difficult, as evidenced by the poor reception of the geography course at the Ecole Normale and the rejection of the last son of the Cassini family by revolutionary and post-revolutionary science. This phase undoubtedly gave rise to the current of hostility to all theory that persisted in French geography for over a century. The wars mobilised the discipline for a generation, encouraging it but also influencing its direction. The geographers of the time were struggling to make sense of their world at a time when public interest was turning towards the study of society and spatial planning, towards the dynamic and often invisible interactions and interconnections among natural phenomena, and towards the exploration of the environment.