From its birth in seventh-century Arabia, Islam has been a faith on the move. In Worlds of Islam, James McDougall explores its origins and transformations from Late Antiquity to the digital age. Over the span of a thousand years, armies, missionaries, and merchants carried it to the edges of Europe, the coasts of Southeast Asia, and the remote interior of China. By the nineteenth century, Islam encompassed a world of great diversity, from Muslim-ruled empires to nations where Muslims lived out their faith among many others. In the twentieth century, while monarchs in the Gulf asserted dynastic privilege and fundamentalists in Egypt and Pakistan preached social morality, revolutionaries from Algeria to Indonesia fought for national self-determination, and activists in North America and Europe campaigned for civil liberties and social justice. As empires fell and new superpowers rose, Muslims proved to be as adaptable and dynamic as modernity itself. Sweeping and authoritative, Worlds of Islam narrates the epic story of how Muslims emerged as a community, built empires, traversed the globe, came to number in the billions, and became modern.