The word "liberalism" is derived from the Latin liber, free. As the name indicates, liberalism is traditionally a political ideology emphasizing the personal liberty of each individual, including freedom of thought, conscience, religion, opinion, expression, assembly, association, movement, enterprise, occupation, contract, etc. which the state should not violate, except to protect the rights of others.

Classical liberalism emerged first in the seventeenth century Europe, and was represented during the following centuries by such thinkers as John Locke, Voltaire, Adam Smith, Immanuel Kant and John Stuart Mill. Beside personal liberty, classical liberalism also advocated economical liberty, the right of property, capitalism and free markets.

In the beginning of the twentieth century, however, the meaning of the word "liberalism" became altered in North America. The "New Liberalism" demanded a much stronger role of state in protecting personal liberty and social justice, in expense of economical liberty. This variant of liberalism is also known as "welfare liberalism" or "social liberalism" or "liberal egalitarianism". Its most famous theorists include American philosophers John Rawls and Ronald Dworkin and British economist John Maynard Keynes.

As the default meaning of the word "liberal" changed in North America, began the American classical liberals call their philosophy "libertarianism" or "market liberalism". Its most notable modern representatives include Austrian economists Ludwig von Mises, Friedrich von Hayek, American economist Milton Friedman and American philosopher Robert Nozick.

In Europe and other parts of the world "liberalism" usually still refers to its more or less classical meaning. Therefore a liberal encountered in Europe more likely supports free market, and a liberal in America more likely defends welfare state. The former would be called a libertarian in America, the latter a social liberal or a social democrat in Europe. In most other languages than English the word "liberalism" refers almost solely to the free market variant of the word.

Because of the varying meanings of the word "Liberalism" this category is divided to two subcategories, "Social Liberalism", which refers to the meaning of liberalism more common in North America, and "Libertarianism", which refers to the meaning of liberalism more common in Europe and other parts of the world.