This book presents groundbreaking new research on a fifteenth-century world map by Henricus Martellus, c. 1491, now at Yale. The importance of the map had long been suspected, but it was essentially unstudiable because the texts on it had faded to illegibility. Multispectral imaging of the map, performed with NEH support in 2014, rendered its texts legible for the first time, leading to renewed study of the map by the author. This volume provides transcriptions, translations, and commentary on the Latin texts on the map, particularly their sources, as well as the place names in several regions. This leads to a demonstration of a very close relationship between the Martellus map and Martin Waldseemüller's famous map of 1507. One of the most exciting discoveries on the map is in the hinterlands of southern Africa. The information there comes from African sources; the map is thus a unique and supremely important document regarding African cartography in the fifteenth century. This book is essential reading for digital humanitarians and historians of cartography.