Left-wing politics is the range of political ideologies that support and seek to achieve social equality and egalitarianism, often in opposition to social hierarchy either as a whole, or of certain social hierarchies. Left-wing politics typically involve a concern for those in society whom its adherents perceive as disadvantaged relative to others as well as a belief that there are unjustified inequalities that need to be reduced or abolished, through radical means that change the nature of the society they are implemented in. According to emeritus professor of economics Barry Clark, supporters of left-wing politics "claim that human development flourishes when individuals engage in cooperative, mutually respectful relations that can thrive only when excessive differences in status, power, and wealth are eliminated."

Within the left–right political spectrum, left and right were coined during the French Revolution, referring to the seating arrangement in the French National Assembly between revolutionaries and monarchists respectively. Usage of the term left became more prominent after the restoration of the French monarchy in 1815, when it was applied to the Independents. The word wing was first appended to left and right factions in the late 19th century, usually with disparaging intent, and left-wing was applied to those who were unorthodox in their religious or political views.

Ideologies considered to be left-wing vary greatly depending on the placement along the political spectrum in a given time and place. At the end of the 18th century, upon the founding of the first liberal democracies, the term Left was used to describe liberalism in the United States and republicanism in France, supporting a lesser degree of hierarchical decision-making than the right-wing politics of the traditional conservatives and monarchists. In modern politics, the term Left typically applies to ideologies and movements to the left of classical liberalism, supporting some degree of democracy in the economic sphere.

Today, ideologies such as social liberalism and social democracy are considered to be centre-left, while the Left is typically reserved for movements more critical of capitalism, including the labour movement, socialism, anarchism, communism, Marxism, and syndicalism, each of which rose to prominence in the 19th and 20th centuries. In addition, the term left-wing has also been applied to a broad range of culturally liberal and progressive social movements, including the civil rights movement, feminist movement, LGBT rights movement, abortion-rights movements, multiculturalism, anti-war movement, and environmental movement, as well as a wide range of political parties.‌

The following positions are typically associated with left-wing politics.

Left-leaning economic beliefs range from Keynesian economics and the welfare state through industrial democracy and the social market to the nationalisation of the economy and central planning, to the anarcho-syndicalist advocacy of a council-based and self-managed anarchist communism. During the Industrial Revolution, leftists supported trade unions. At the beginning of the 20th century, many leftists advocated strong government intervention in the economy. Leftists continue to criticise the perceived exploitative nature of globalisation, the "race to the bottom" and unjust lay-offs and exploitation of workers. In the last quarter of the 20th century, the belief that the government (ruling in accordance with the interests of the people) ought to be directly involved in the day-to-day workings of an economy declined in popularity amongst the centre-left, especially social democrats who adopted the Third Way. Left-wing politics are typically associated with popular or state control of major political and economic institutions.

Other leftists believe in Marxian economics, named after the economic theories of Karl Marx. Some distinguish Marx's economic theories from his political philosophy, arguing that Marx's approach to understanding the economy is independent of his advocacy of revolutionary socialism or his belief in the inevitability of a proletarian revolution. Marxian economics do not exclusively rely on Marx and draw from a range of Marxist and non-Marxist sources. The dictatorship of the proletariat and workers' state are terms used by some Marxists, particularly Leninists and Marxist–Leninists, to describe what they see as a temporary state between the capitalist state of affairs and a communist society. Marx defined the proletariat as salaried workers, in contrast to the lumpenproletariat, who he defined as the outcasts of society such as beggars, tricksters, entertainers, buskers, criminals and prostitutes. The political relevance of farmers has divided the left. In Das Kapital, Marx scarcely mentioned the subject. Mikhail Bakunin thought the lumpenproletariat was a revolutionary class, while Mao Zedong believed that it would be rural peasants, not urban workers, who would bring about the proletarian revolution.

Left-libertarians, anarchists and libertarian socialists believe in a decentralised economy run by trade unions, workers' councils, cooperatives, municipalities and communes, opposing both state and private control of the economy, preferring social ownership and local control in which a nation of decentralised regions is united in a confederation. The global justice movement, also known as the anti-globalisation movement and the alter-globalisation movement, protests against corporate economic globalisation due to its negative consequences for the poor, workers, the environment, and small businesses.