Socialist economic systems can be divided into non-market and market forms. Non-market socialism involves the substitution of factor markets and money, with engineering and technical criteria, based on calculation performed in-kind, thereby producing an economic mechanism that functions according to different economic laws from those of capitalism. Non-market socialism aims to circumvent the inefficiencies and crises traditionally associated with capital accumulation and the profit system. By contrast, market socialism retains the use of monetary prices, factor markets and in some cases the profit motive, with respect to the operation of socially owned enterprises and the allocation of capital goods between them. Profits generated by these firms would be controlled directly by the workforce of each firm, or accrue to society at large in the form of a social dividend. The socialist calculation debate discusses the feasibility and methods of resource allocation for a socialist system.
The socialist political movement includes a set of political philosophies that originated in the revolutionary movements of the mid-to-late 18th century and of concern for the social problems that were associated with capitalism. In addition to the debate over markets and planning, the varieties of socialism differ in their form of social ownership, how management is to be organised within productive institutions and the role of the state in constructing socialism. Core dichotomies include reformism versus revolutionary socialism and state socialism versus libertarian socialism. Socialist politics has been both centralist and decentralised; internationalist and nationalist in orientation; organised through political parties and opposed to party politics; at times overlapping with trade unions and at other times independent of—and critical of—unions; and present in both industrialised and developing countries. While all tendencies of socialism consider themselves democratic, the term "democratic socialism" is often used to highlight its advocates' high value for democratic processes in the economy and democratic political systems, usually to draw contrast to tendencies they may perceive to be undemocratic in their approach. Democratic socialism is frequently used to draw contrast to the political system of the Soviet Union, which critics argue operated in an authoritarian fashion.
By the late 19th century, after the work of Karl Marx and his collaborator Friedrich Engels socialism had come to signify opposition to capitalism and advocacy for a post-capitalist system based on some form of social ownership of the means of production. By the 1920s, social democracy and communism had become the two dominant political tendencies within the international socialist movement. By this time, socialism emerged as "the most influential secular movement of the twentieth century, worldwide. It is a political ideology (or world view), a wide and divided political movement" and while the emergence of the Soviet Union as the world's first nominally socialist state led to socialism's widespread association with the Soviet economic model, many economists and intellectuals argued that in practice the model functioned as a form of state capitalism or a non-planned administrative or command economy. Socialist parties and ideas remain a political force with varying degrees of power and influence in all continents, heading national governments in many countries around the world. Today, some socialists have also adopted the causes of other social movements, such as environmentalism, feminism and liberalism.
The origin of the term "socialism" may be traced back and attributed to a number of originators, in addition to significant historical shifts in the usage and scope of the word.
For Andrew Vincent, "he word ‘socialism’ finds its root in the Latin sociare, which means to combine or to share. The related, more technical term in Roman and then medieval law was societas. This latter word could mean companionship and fellowship as well as the more legalistic idea of a consensual contract between freemen".