Collectivism describes any outlook or philosophy that stresses the interactivity between people. It is often considered the opposite of individualism, though both individualism and collectivism can be important within a single outlook. In a collective philosophy, the group or society is seen as having precedence over the individual.

There are two basic types of collectivism: horizontal and vertical. In horizontal collectivism, members of the collective are considered to be as equal as possible, sharing resources and responsibilities. In the vertical variety, there is a social hierarchy that society members work to maintain, and people submit to those above them in the hierarchy.

Collectivism is perhaps best known as one of the philosophies behind socialism. Communist and fascist societies have been described as collectivist, or more specifically as forms of vertical collectivism. Early collectivist political thought, exemplified by Jean-Jacques Rousseau’s 1762 Social Contract, was more horizontal or democratic in nature. Rousseau's work eventually inspired both communism and democracy.

While the writings of Rousseau and Marx, along with most socialist and democratic communities in practice, rely on the government to represent the will of the people, this is not a necessary component of a collectivist system. For example, collectivist anarchism calls for no government or private property ownership, but rather small communes that own collective property. Small horizontal collectivist communities likewise may not have any leader or centralized authority. An example of such a community is the Israeli kibbutzim, small farming communities in which people voluntarily share all labor and property.

Criticisms against collectivism often take the line that it is at the expense of the individual. Collectivist thought may promote a certain group identity to the point of stifling diversity. It also carries the danger of extreme statism, in which the government or political entity controls every aspect of the economy and society, and in which the people exist to serve the government rather than vice versa. Stalinism and fascism are two of the best known examples of such extreme statism.

Most political and social systems, in both theory and practice, contain a blend of collectivism and individualism. For example, in the present day United States, individuals can own property, but local, state, and federal governments fund some public social programs. Most thinkers agree that both the individual and the community are important to society. Disagreement stems from the nature and level of importance designated to each.