In general, Leftists are people who hold equality as their principle political value. Originally, leftists were people who opposed monarchy and supported democracy, because they wanted everyone to have an equal role in making political decisions. Socialists and Communists are universally considered left-wing, because they support economic equality. Movements that advocate for the social equality of disempowered groups, like women, immigrants, racial minorities, and LGBTQ people, are also usually considered left-wing.

In the US, the Democratic party is the more left-wing of the two main parties and is sometimes included under the "leftist" umbrella. However, some people, mostly on the far-left, reserve the term "leftist" for those who oppose capitalism.