Syndicalism is a labor movement within society that, through industrial unionism, seeks to unionize workers according to industry and advance their demands through strikes and other forms of direct action, with the eventual goal of gaining control over the means of production and the economy at large through social ownership.

Syndicalist unions first emerged in Spain and North America in the 1870s, before rising to prominence in France and later emerging on other continents. Syndicalist movements were most predominant amongst the socialist movement during the interwar period that preceded the outbreak of World War II. Major syndicalist organizations included the General Confederation of Labor (CGT) in France, the Confederacion Nacional del Trabajo (CNT) in Spain, the Italian Syndicalist Union (USI), the Free Workers' Union of Germany (FAUD), and the Argentine Regional Workers' Federation (FORA). Although they did not regard themselves as syndicalists, the Industrial Workers of the World (IWW) (nicknamed "Wobblies") in the United States, the Irish Transport and General Workers' Union (ITGWU), and the Canadian One Big Union (OBU) are considered by most historians to belong to this movement^{[citation needed]}.

The International Workers' Association – Asociación Internacional de los Trabajadores (IWA–AIT), which was formed in 1922, is an international syndicalist federation of various labour unions from different countries. At its peak, it represented millions of workers and competed directly for the hearts and minds of the working class with social democratic unions and parties. A number of syndicalist organizations were and still are to this day linked in the IWA–AIT; some of its member organizations left for the International Confederation of Labour (ICL–CIT), which was formed in 2018.

The word syndicalism has French origins. In French, a syndicat is a trade union, usually a local union. A syndicate is a self organizing group working towards a shared interest. The corresponding words in Spanish and Portuguese, sindicato, and Italian, sindacato, are similar. By extension, the French syndicalisme refers to trade unionism in general. The concept of syndicalisme révolutionnaire or revolutionary syndicalism emerged in French socialist journals in 1903, and the French General Confederation of Labor (Confédération générale du travail, CGT) came to use the term to describe its brand of unionism. Revolutionary syndicalism, or more commonly syndicalism with the revolutionary implied, was then adapted to a number of languages by unionists following the French model.

Many scholars, including Ralph Darlington, Marcel van der Linden, and Wayne Thorpe, apply syndicalism to a number of organizations or currents within the labor movement that did not identify as syndicalist. They apply the label to one big unionists or industrial unionists in North America and Australia, Larkinists (named after the Irish ITGWU leader James Larkin) in Ireland, and groups that identify as revolutionary industrialists, revolutionary unionists, anarcho-syndicalists, or councilists. This includes the Industrial Workers of the World (IWW) in the United States, which claimed its industrial unionism was "a higher type of revolutionary labor organization than that proposed by the syndicalists". Van der Linden and Thorpe use syndicalism to refer to "all revolutionary, direct-actionist organizations". Darlington proposes that syndicalism be defined as "revolutionary trade unionism". He and van der Linden argue that it is justified to group together such a wide range of organizations because their similar modes of action or practice outweigh their ideological differences.

Others, such as Larry Peterson and Erik Olssen, disagree with this broad definition. According to Olssen, this understanding has a "tendency to blur the distinctions between industrial unionism, syndicalism, and revolutionary socialism". Peterson gives a more restrictive definition of syndicalism based on five criteria:

This definition excludes the IWW and the Canadian One Big Union (OBU), which sought to unite all workers in one general organization. Peterson proposes the broader category revolutionary industrial unionism to encompass syndicalism, groups like the IWW and the OBU, and others.

Revolutionary industrial unionism, part of syndicalism in the broader sense, originated with the IWW in the United States and then caught on in other countries. In a number of countries, certain syndicalist practices and ideas predate the coining of the term in France or the founding of the IWW. In Bert Altena's view, a number of movements in Europe can be called syndicalist, even before 1900. According to the English social historian E. P. Thompson and the anarcho-syndicalist theorist Rudolf Rocker, there were syndicalist tendencies in Britain's labor movement as early as the 1830s. Syndicalism's direct roots were in Pierre-Joseph Proudhon's mutualism, a form of socialism that focused on cooperation among the community of man. He coined capitalist to describe the political class granting itself monopolies on the use of capital, and wanted workers to oppose this state control through peaceful means, only using force defensively. Proudhon's ideas were popular in the anti-authoritarian wing of the early International Workingmen's Association (IWA), the first international socialist organization, formed in 1864. Its most successful early leader, Russian anarchist Mikhail Bakunin, came to believe that worker organizations should consider using force to advance their cause, when necessary. He and his followers advocated the general strike, rejected electoral politics, and anticipated workers' organizations replacing rule by the state, central syndicalist themes.