The offshore wind energy sector in the United Kingdom (UK) has grown rapidly since the first turbine generators were installed in 2000: by 2016 there were over 1400 installed turbines with combined capacity of 5.1 GW. The sector is considered by UK Government as essential to the development of a low carbon economy and to meeting binding targets on carbon reduction and renewable energy generation. The Crown Estate, responsible for licensing development on the sea bed around the UK, has held three rounds of licensing since 2000 for wind developments. Some of the projects in the first two rounds suffered long delays due to uncertainty of project level impacts, particularly cumulative impacts. A number of key stakeholders identified a need for cumulative impact assessment (CIA) methodology to be developed that was definitive and endorsed by regulators and industry to aid unblocking barriers to delivery. This paper explores the background to the development of the guidelines and how they were ‘co-created’ with industry and regulators. We evaluate to what extent they have been used to shape and develop practice.