Margaret Thatcher (1925–2013) was the United Kingdom's prime minister from 1979 to 1990. Her informal transatlantic alliance with U.S. President Ronald Reagan from 1981 to 1989 played an important role in the promotion of an international neoliberal policy agenda that remains influential today. Her critique of UK social democracy during the 1970s and her adoption of key neoliberal strategies, such as financial deregulation, trade liberalization, and the privatization of public goods and services, were popularly labeled Thatcherism. In this article, we consider the nature of Thatcherism and its impact on health and well-being during her period as prime minister and, to a lesser extent, in the years that follow; we focus mainly on Great Britain (England, Scotland, and Wales). Thatcher's policies were associated with substantial increases in socioeconomic and health inequalities: these issues were actively marginalized and ignored by her governments. In addition, her public-sector reforms applied business principles to the welfare state and prepared the National Health Service for subsequent privatization.