It was formed in accordance with the (then) Department of the Environment's 'Northern Ireland Waste Management Strategy' at that time which promoted the concept of a joint approach between councils in geographical sub-regions across Northern Ireland.
In 2003, arc21's constituent councils signed a Collaboration Agreement (Terms of Agreement) which forms the basis of arc21's legal status as a body corporate. This has been augmented by a Supplementary Agreement in 2009. The Supplementary Agreement can be viewed in the Finance and Governance file category in the Downloads section.
Since local government reform on 1 April 2015, an updated Collaboration Agreement (Terms of Agreement), was signed by the six constituent councils which supersedes the 2003 agreement.