A social movement is a collective action taken by a group of people to tackle social problems. Of course, the nature and character of different social movements are quite diverse. While social movements of the past were exemplified by labor movements and socialist movements, the goals and values of present-day social movements are highly varied and include such issues as the environment, anti-war and peace, women's rights, minority rights, grass-roots movements focusing on local or regional issues, and consumer rights. The methods utilized are also varied, ranging from demonstrations, meetings, petitions, media campaigns, boycotts, to violent actions. With the increasing globalization, the number of transnational social movements reaching across national borders is also growing.

In earlier research, the rise of social movements was explained by factors related to social structure. This trend is illustrated by the attribution by Marxist theory of the rise of labor unions to inherent contradictions in Capitalism and the proposal by collective behavior theory that the stresses and dissatisfaction resulting from sudden changes in society cause people to take extreme actions. The perspective that social movements simply arise in response to dissatisfaction, however, was significantly revised with the emergence of "resource mobilization theory" in the 1970s. Resource mobilization theory focuses on resources including leadership, financial resources and networks that are necessary for social movement organizations to conduct their activities. The gist of resource mobilization theory is that while dissatisfaction exists in all societies, social movements occur only when sufficient resources are available. From the standpoint of access of the movement to external resources, the "political opportunity structure" has been a point of focus. That is to say, the political context -- the openness of the policy-making process, the presence of influential allies, and conflicts among political elites -- can significantly impact the emergence and trajectory of a social movement. In addition, "framing," which assigns meaning to events or actions or provides a world view, is important in mobilizing support for a social movement.

The theory of social movements has been developed primarily based on the experiences in developed countries. Social movements, however, are not irrelevant to developing countries. In the developing world, historically, social movements occurred as a form of protest against colonial rule and imperial invasion. In recent years, social movements have arisen around the world in the form of democratization movements protesting military or single-party rule, or movements based on religious values, for example, so-called "Islamic fundamentalism" . In addition, regarding basic necessities such as housing, land, water, and health care, social movements have emerged, either demanding political measures or solving the issues themselves through organizing. The World Social Forum, with the slogan "Another World is Possible," has served, since its first convening in 2001 as a protest to the Davos meeting of the World Economic Forum, as an annual forum for social activists from around the world to meet and exchange ideas and experiences.