ISA was founded in 1974 as the Committee for a Workers' International (CWI), by supporters of Militant from 12 countries.

Following a split in 2019, in which one side continued under the name CWI, the group renamed itself International Socialist Alternative.In 2018 and 2019, a dispute developed in the organization around the questions of socialists being part of feminist and LGBT movements,[1][2] the role of the trade unions and the working-class movement, and under what programme and how Marxists ought to organize internationally and domestically.

[10][11] The faction's leadership was concentrated in the Socialist Party (England and Wales), which was the largest section of the CWI, as a number of members served on both the leading body of the England & Wales section and on the IS, including its general secretary, Peter Taaffe.

The IEC outlined a process of discussion and debate to avoid a split, leading to a World Congress in January 2020, the highest decision-making body of the CWI.

[16][17] At the CWI Majority World Congress on 1 February 2020, the name of the organisation was changed to International Socialist Alternative.

[21] The reasons cited included a disagreement in the approach to use of online media, and a turn toward Taiwanese nationalism by International Socialist Forward.

[23] These organisations later published the rationale for their split, including the many documents relating to their debate with the ISA majority on their website.

[26] In addition to the work carried out across its various national sections, the ISA also runs three international campaigns.

Peng's whereabouts and safety have become a matter of international concern after she early this month disappeared after she accused former Chinese vice premier Zhang Gaoli of sexual abuse.

[30][31] The campaign insists that it is capitalism which is destroying the planet so what is needed is large scale, system changes — otherwise the effects of global warming will be out of control.

[33] spokesperson Danny Said "We need to make sure that COP26 can hear the voice of the working class” [34] As part of the current subversion trial the Chinese regime has rounded up almost the entire crop of opposition leaders and proposed candidates, from across the spectrum of anti-government politics, including trade unionists, pro-Western liberals and localists (a Hong Kong nationalist movement).

[35] The campaign claims "the best support for the democracy struggle will come from inspiring grassroots solidarity — from labour, social and civil rights movements who are fighting on behalf of the oppressed and disenfranchised in their own societies.

To fight repression and authoritarian rule in Hong Kong — and China — we need people’s solidarity across national borders.