This chapter presents new, annotated translations of the extensive summaries and paraphrases of books 1 and 5 of Agatharchides’ lost work On the Erythraian Sea (written c.145 BC) that were made by Diodoros (book 3), Strabo (book 16), and especially Photios (Bibliotheke, codices 213 and 250). Additional testimonia and fragments are arranged as five extracts. The chapter introduction reviews Agatharchides’ career, his writings, and his scholarly milieux in Alexandria and later (probably) Athens, and upholds the view that On the Erythraian Sea was a self-contained work, not part of a larger whole. The geographical and ethnographic material in this work–a historical work–is distinctive for being based on information from Ptolemaic commanders and explorers, and remarkable for its sympathy with some of the Ptolemies’ oppressed subjects. Agatharchides’ depiction of these peoples implies an evolutionary scheme of development–from hunter-gatherers to pastoralists to farmers–such as Dikaiarchos (Chapter 9 of this volume) had suggested in his philosophical works. The surviving summaries include remarkable passages on elephant-hunting and the sufferings of gold-miners; but Agatharchides’ work was more often accessed through its reworking by Artemidoros (Chapter 18) than read in its own right. A new map highlights the principal places and peoples mentioned by Agatharchides in East Africa and Arabia.