The National Insurance Act 1911 created National Insurance, originally a system of health insurance for industrial workers in Great Britain based on contributions from employers, the government, and the workers themselves. It was one of the foundations of the modern welfare state. It also provided unemployment insurance for designated cyclical industries. It formed part of the wider social welfare reforms of the Liberal Governments of 1906–1915, led by Henry Campbell-Bannerman and H. H. Asquith. David Lloyd George, the Liberal Chancellor of the Exchequer, was the prime moving force behind its design, negotiations with doctors and other interest groups, and final passage, assisted by Home Secretary Winston Churchill.

National Insurance (NI) is a fundamental component of the welfare state in the United Kingdom. It acts as a form of social security, since payment of NI contributions establishes entitlement to certain state benefits for workers and their families.