A mixed economy is variously defined as an economic system blending elements of a market economy with elements of a planned economy, markets with state interventionism, or private enterprise with public enterprise. Common to all mixed economies is a combination of free-market principles and principles of socialism. While there is no single definition of a mixed economy, one definition is about a mixture of markets with state interventionism, referring specifically to a capitalist market economy with strong regulatory oversight and extensive interventions into markets. Another is that of active collaboration of capitalist and socialist visions. Yet another definition is apolitical in nature, strictly referring to an economy containing a mixture of private enterprise with public enterprise. Alternatively, a mixed economy can refer to a reformist transitionary phase to a socialist economy that allows a substantial role for private enterprise and contracting within a dominant economic framework of public ownership. This can extend to a Soviet-type planned economy that has been reformed to incorporate a greater role for markets in the allocation of factors of production.

The idea behind a mixed economy, as advocated by John Maynard Keynes and several others, was not to abandon the capitalist mode of production but to retain a predominance of private ownership and control of the means of production, with profit-seeking enterprise and the accumulation of capital as its fundamental driving force. The difference from a laissez-faire capitalist system is that markets are subject to varying degrees of regulatory control and governments wield indirect macroeconomic influence through fiscal and monetary policies with a view to counteracting capitalism's history of boom and bust cycles, unemployment, and economic inequality. In this framework, varying degrees of public utilities and essential services are provided by the government, with state activity providing public goods and universal civic requirements, including education, healthcare, physical infrastructure, and management of public lands. This contrasts with laissez-faire capitalism, where state activity is limited to maintaining order and security, and providing public goods and services, as well as the legal framework for the protection of property rights and enforcement of contracts.

About Western European economic models as championed by conservatives (Christian democrats), liberals (social liberals), and socialists (social democrats - social democracy was created as a combination of socialism and liberal democracy) as part of the post-war consensus, a mixed economy is in practice a form of capitalism where most industries are privately owned but there is a number of utilities and essential services under public ownership, usually around 15 to 20 percent. In the post-war era, Western European social democracy became associated with this economic model. As an economic ideal, mixed economies are supported by people of various political persuasions, in particular social democrats. The contemporary capitalist welfare state has been described as a type of mixed economy in the sense of state interventionism, as opposed to a mixture of planning and markets, since economic planning was not a key feature or component of the welfare state.