This is a book-length version of Andrew Watson's groundbreaking 1974 Journal of Economic History article. There he noted a fundamental transformation preceding "The Columbian Exchange" described by Alfred Crosby. Islam unified much of the Middle East and Asia, enabling the transfer of valuable plants and farming techniques within the Muslim world. Some crops, such as sorghum from Africa, traveled farther east. But many others came west to enrich the diets and economies of the Mediterranean, Europe and ultimately the Americas several centuries later. These included most citrus fruits, mangos, Asiatic rice and especially cotton and sugar cane, which both led to major changes in economy, population distribution and vegetation cover. Knowledge and technology transfer included a variety of sophisticated irrigation methods and new forms of land tenure. Watson's article deftly outlined the process; the book is not a complete transition to the fuller genre and resembles an extended essay, but adds detail in cataloging crops and techniques. What he first called "the Arab agricultural revolution" is more properly dubbed Islamic here, since many non-Arabs contributed to the innovations. Overall, Watson identifies a crucial development in world history that is still neglected---perhaps because the book was not in print very long.