Is there any need to go back to Columbus yet again? Science journalist Charles Mann thinks so, though not for the usual purpose. He first went back to 1492 in fact six years ago with his book 1491, a survey of the rich ecology of Native life in the Americas just before its isolation ended. That book was a memorial to the world we lost when the Americas were integrated with Europe, Africa and Asia. 1493 presents us with the world we gained as a result. The book is not really about 1493 nor, thankfully, 1492. Mann does quickly revisit the Columbus fetish, but he soon moves on to explore what happened through later centuries as the New World became part of the world. His guide in this project is Alfred Crosby. Four decades ago Crosby published his first book on what he dubbed the ‘Columbian exchange’, the movement of microbes and other biota into and out of the Americas subsequent to Columbus’s landfall. A second book a decade later explored the ecological rearrangement of the globe produced by these movements, coining the equally memorable term ‘ecological imperialism’. Mann not only acknowledges his debt to Crosby but sought him out. When he urged his mentor to pull together the new environmental history that has since been done and bring his work up to date, Crosby countered with the suggestion that Mann take up the task – hence this book.