The dominant political and economic outlook of 19th-century Britain and, in modified forms, much of the West. Classical liberalism is defined less by a single doctrine than by a cluster of commitments: individual liberty, limited and constitutional government, rule of law, freedom of conscience and speech, toleration, free trade, and property rights as a bulwark against arbitrary power.
Its intellectual lineage runs from John Locke (natural rights, consent, resistance to tyranny) through the Scottish Enlightenment — Adam Smith above all — to the great Victorian synthesizers John Stuart Mill, Richard Cobden, and John Bright. Politically it animated the anti-slavery movement, the repeal of the Corn Laws, Catholic emancipation, and successive extensions of the franchise.
Classical liberals were not libertarians in the modern sense. Most accepted a role for the state in education, public health, and infrastructure; Mill himself drifted toward socialism late in life. But they shared a default suspicion of concentrated power — whether royal, ecclesiastical, aristocratic, or (later) corporate and bureaucratic.
The tradition fractured in the late 19th and early 20th centuries as "new liberalism" (T.H. Green, Hobhouse, Keynes) accepted a much larger role for the state, while a rump of market-focused thinkers became the ancestors of modern libertarianism and Neoliberalism.