The London Energy Transformation Initiative (LETI) was established in 2017 to support the transition of the capital’s built environment to net zero carbon, providing guidance that can be applied to the rest of the United Kingdom (UK). We do this by: → Engaging with stakeholders to develop a robust and rapid energy reduction approach, producing effective solutions to the energy trilemma of security, sustainability, and affordability; → Working with local authorities to create practicable policy alterations to ensure the regulatory system is ft for purpose, placing verified performance at its core; → Encouraging and enabling collaboration within a large, diverse group of built environment professionals; and → Providing technical advice to support exemplar developments, enabling leader who want to deliver net zero carbon buildings. LETI is a network of over 1,000 built environment professionals who are working together to put London on the path to a zero carbon future. The voluntary group is made up of dedicated and passionate developers, engineers, housing association professionals, architects, planners, academics, sustainability professionals, contractors, and facilities managers, with support and input provided by the Greater London Authority (GLA) and London boroughs. LETI was established for these groups to work collaboratively to put together evidence-based recommendations for two pieces of policy – the new London Environment Strategy and the rewrite of the London Plan (planning policy uidance published by the GLA). Many of the recommendations that LETI put forward to the GLA have been included in emerging London policy and Energy Assessment Guidance.Over the last year LETI has focused on providing this guidance on defining what good looks like in the context of the climate emergency for new buildings. For more information on LETI, please see www.LETI.uk @LETI_UK