Michael Bennett provides the first history of the global spread of vaccination during the Napoleonic Wars, offering a new assessment of the cowpox discovery and Edward Jenner’s achievement in making cowpox inoculation a viable and universally available practice. He explores the networks that took the vaccine around the world, and the reception and establishment of vaccination among peoples in all corners of the globe. His focus is on the human story of the horrors of smallpox, the hopes invested in vaccination by medical men and parents, the children put arm-to-arm across the world, and the early challenges, successes and disappointments. He presents vaccination as a quiet revolution, genuinely emancipatory, but also the sharp end of growing state power. By the end of the war in 1815, millions of children had been vaccinated. The early success of the war against smallpox paved the way to further advances towards eradication.