Chapter 4 discusses the expansion of vaccination in the British Isles during the Napoleonic Wars. The rapid extension of the practice from 1800, involving hundreds of thousands of people, represented a mobilisation of opinion and action that paralleled the mobilisation of the nation for war. Medical men took up vaccination with alacrity, seeking to make their name and serve their communities. Members of the aristocracy and gentry, with women often in the lead, accepted it in their families and supported it in their spheres of influence. Clergymen promoted it from the pulpit. Reckless practice led to adverse outcomes that encouraged anxieties about inoculating cowpox and provided ammunition for an anti-vaccination movement in London in 1805–7. Instructed to conduct an enquiry, the College of Physicians fully endorsed vaccination in 1807. After receiving the report, Parliament broke new ground in health provision by funding a National Vaccine Establishment to distribute vaccine and have oversight of the practice.