Thatcherism is the system of political thought attributed to the governments of Margaret Thatcher, British Prime Minister during the 1980s.

The key attributes of Thatcherism (as well as the term Thatcherism itself) were identified and articulated by Professor Stuart Hall and Martin Jacques. Through the influential theoretical journal Marxism Today, their subsequent work created the intellectual underpinnings of what was to become New Labour.

Ms Thatcher was unusual in late twentieth century British politics in being a highly ideological leader. She once thumped a copy of The Constitution of Liberty, by Friedrich Hayek upon the dispatch box in the House of Commons, proclaiming: "This is what we believe". Thatcherism is characterized by a free market economy perhaps more closely associated with Victorian Liberalism in the United Kingdom, monetarist economic policy, privatization of state-owned industries, low taxation, opposition to trade unions and a check on the size of the Welfare State. Thinkers closely associated with Thatcherism include Keith Joseph and Milton Friedman. Thatcherism was strongest in south east England, the wealthiest region of the United Kingdom, and the greatest beneficiary of Thatcherite policy. After the initial shock and the recession of the early 1980s, the finance sector of Britain's economy began to revive, though it faced a second recession in the late 1980s. The collapse of Britain's manufacturing base, which many blame on Thatcherism, was partly compensated for by the growth in the service industries.

Changes to the power of the Trade Unions were made gradually unlike the approach of the Heath Government, and the greatest single confrontation with the unions was the NUM strike of 1984 to 1985 in which the union eventually had to concede.

Whether it ultimately benefited Britain or not, it destroyed the post-war consensus of British politics. In 2001 Peter Mandelson, a member of parliament belonging to the British Labour Party closely associated with Tony Blair, famously declared that "we are all Thatcherites now". Nonetheless, many people continue to use the word "Thatcherism" as a term of abuse.

Towards the end of the 1980s, Thatcherism was stubborn in its opposition to perceived attempts by the European Union to erode British sovereignty. In a famous 1988 Bruges speech, Thatcher declared that "We have not successfully rolled back the frontiers of the state in Britain, only to see them reimposed at a European level, with a European super­state exercising a new dominance from Brussels."

Thatcherism may be compared with Reaganomics and Rogernomics.