The history of the socialist movement in the United States spans a variety of tendencies, including anarchists, communists, democratic socialists, social democrats, Marxists, Marxist–Leninists, Trotskyists and utopian socialists. It began with utopian communities in the early 19th century such as the Shakers, the activist visionary Josiah Warren and intentional communities inspired by Charles Fourier. Labor activists, usually Jewish, German, or Finnish immigrants, founded the Socialist Labor Party of America in 1877. The Socialist Party of America was established in 1901. By that time, anarchism also rose to prominence around the country. Socialists of different tendencies were involved in early American labor organizations and struggles. These reached a high point in the Haymarket massacre in Chicago, which founded the International Workers' Day as the main labour holiday around the world, Labor Day and making the eight-hour day a worldwide objective by workers organizations and socialist parties worldwide.

Social democracy is a political, social, and economic philosophy within socialism that supports political and economic democracy and supports a gradualist, reformist and democratic approach towards achieving socialism, usually under a social liberal framework. In practice, social democracy takes a form of socially managed welfare capitalism, achieved with partial public ownership, economic interventionism, and policies promoting social equality.