Today, alphabetical order seems like a common-sense way of arranging data, but it was not always considered valid. Samuel Pepys, Denis Diderot, and George Washington were early proponents, but many others stuck to older forms of classification—Yale listed its students by their family's social status until 1886. And yet, while the order of the alphabet now rules—libraries, phone books, reference books, even the order of entry for the teams at the Olympic Games—it has remained curiously invisible. With wry humor, Judith Flanders traces the triumph of alphabetical order and offers a compendium of Western knowledge, from A to Z.