In 1972, Alfred Crosby published a small work that illuminated a simple point, that the most important changes brought on by the voyages of Columbus were not social or political, but biological in nature. The book told the story of how 1492 sparked the movement of organisms, both large and small, in both directions across the Atlantic. This "Columbian exchange," between the Old World and the New, changed the history of our planet drastically and forever. The book "The Columbian Exchange" changed the field of history drastically and forever as well. It has become one of the foundational works in the burgeoning field of environmental history, and it remains one of the canonical texts for the study of world history. This 30th anniversary edition includes a new preface from the author, reflecting on the book and its creation, and a new foreword by J.R. McNeill that demonstrates how Crosby established a brand new perspective for understanding ecological and social events. As the foreword indicates, "The Columbian Exchange" remains a vital book, a small work that contains within the inspiration for future examinations into what happens when two peoples, separated by time and space, finally meet.