Left-wing politics describes the range of political ideologies that support and seek to achieve social equality and egalitarianism, often in opposition to social hierarchy. 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. 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 Estates General. Those who sat on the left generally opposed the Ancien Régime and the Bourbon monarchy and supported the Revolution, the creation of a democratic republic and the secularisation of society while those on the right were supportive of the traditional institutions of the Ancien Régime. 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 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 of the Overton window 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 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.