The Alliance for Green Socialism (AGS) is a socialist and environmentalist political grouping operating across the United Kingdom (although its most active membership is in West Yorkshire, particularly in Leeds). It was formed in 2003 following a merger between the Leeds Left Alliance (formed by Mike Davies, Celia Foote, Garth Frankland and other former members of the Labour Party) and the Green Socialist Network (whose origins lie in the former Communist Party of Great Britain). The Leeds Left Alliance had previously been involved in the former Socialist Alliance and a small number of AGS members remained involved in it until it was dissolved by the SWP (who had effectively taken it over) in February 2005. The AGS sponsored an attempt by the Socialist Alliance Democracy Platform to re-form the Socialist Alliance in 2005 but this has had limited success and the group which continues under this name now has a mutual affiliation with the larger AGS.
The AGS describes itself as an Alliance rather than as a Party. This is seen as significant by some AGS members because the AGS contains people from a variety of trends, traditions and ideological backgrounds who have all agreed to work together in a single organisation whilst retaining the right to disagree on some issues. Many of the AGS's members come from former political parties which had a Democratic Centralist tradition while others were formerly in the Labour Party or in no party at all. To argue out every issue on which differences existed to the point where a majority decision was reached which was then binding on all members might lead to many comrades leaving. The current arrangement recognises that the AGS is open to people from various leftist and environmentalist positions - as long as they agree on the basic principles on which the AGS was founded.
The AGS stood candidates in its own name in the Yorkshire and the Humber constituency in the 2004 European Election , coming last with 0.9% of the votes cast. It later contested the 2005 UK general election under its own name and in association with other leftist parties in the Socialist Green Unity Coalition, standing candidates in Yorkshire, London and Brighton.