The World Social Forum (WSF; Portuguese: Fórum Social Mundial [ˈfɔɾũ sosi'aw mũdʒiˈaw]) is an annual meeting of civil society organizations, first held in Brazil, which offers a self-conscious effort to develop an alternative future through the championing of counter-hegemonic globalization.

The World Social Forum can be considered a visible manifestation of global civil society, bringing together non governmental organizations, advocacy campaigns, and formal and informal social movements seeking international solidarity. The World Social Forum prefers to define itself as "an open space – plural, diverse, non-governmental and non-partisan – that stimulates the decentralized debate, reflection, proposal building, experiences exchange and alliances among movements and organizations engaged in concrete action towards a more solidary, democratic and fair world; a permanent space and process to build alternatives to neoliberalism."

The World Social Forum is held by members of the alter-globalization movement (also referred to as the global justice movement) who come together to coordinate global campaigns, share and refine organizing strategies, and inform each other about movements from around the world and their particular issues. The World Social Forum is explicit about not being a representative of all of those who attend and thus does not publish any formal statements on behalf of participants. It tends to meet in January at the same time as its "great capitalist rival", the World Economic Forum's Annual Meeting in Davos, Switzerland. This date is consciously picked to promote alternative answers to world economic problems in opposition to the World Economic Forum.

The World Social Forum first met in 2001, but it had its roots in Latin American activism, namely the encuentro, a meeting which emphasizes dialogue and exchange of ideas among activists. Some of the founders of the WSF, were part of the First International Encuentro for Humanity and Against Neoliberalism in 1996, and decided to expand the idea and make it a global forum for activists of all stripes opposing hegemonic globalization and neoliberalism.

The World Social Forum can also part, trace its tradition of activism back to the Battle for Seattle November 1999, where anti-globalization activists protested a meeting of the World Trade Organization's latest trade negotiations.

One of the originators of the World Social Forum, Oded Grajew, of the Ethos Institute for Business and Social Responsibility, said in an interview with InMotion Magazine in 2004, "Then I had the idea. Why not create the World Social Forum, as we have the World Economic Forum, speaking about the people in the world? Why not have the World Social Forum—the social is more important than the economic—to have a space to show that we can have an alternative? We have choice. This is not the only way you can see the world, globalization. We have another way to see it. And, at the same time, force people to look, to make a choice. What is your choice? What is your vision of the world?"

Another one of the founders of the WSF, Cándido Grzybowski has said of the annual meetings, "The numerous recent crises are expressions of the contradictions and limitations of the form of global capitalism that has been imposed on humanity and the earth. The assertion that "another world is possible" is now an absolute necessity."

Since 2001, the United Nations has had a presence at the WSF through UNESCO, showing the institutional credibility achieved by the forum, seen by UNESCO as a "prime opportunity for dialogue and a laboratory of ideas for the renewal of public policies" through "critical reflection on the future of societies we want to create and for elaborating proposals in search of solidarity, justice, peace and human rights".