Most of the world's population now lives in cities, which are already responsible for 80% of the world's carbon emissions. London's energy use soared during the 2003 heatwave - such extreme temperatures are predicted to be a regular occurrence by the 2050s. Our ageing urban infrastructure needs transformation to withstand the 21st century climate, without worsening it by increased use of energy. But buildings in urban areas don't just withstand local climate: they change it. This interaction is not generally recognised by engineers and planners working to transform urban infrastructure, partly because the science on which design standards are based does not incorporate understanding of urban climate. Adaptation of existing and new buildings to withstand warmer futures sustainably needs both legislation and standards - but policy cannot be formulated without evidence. Planning for sustainable cities on the basis of local climate has been hampered by lack of representative data. This is partially due to the difficulties of making representative full-scale measurements in urban areas with traditional, ground-based methods. Remote sensing techniques - using lasers and sound pulses to probe the air above the buildings at a distance - can provide a cutting-edge solution to the problem. The aim of this proposal is create the Advanced Climate Technology Urban Atmospheric Laboratory (ACTUAL), consisting of the tools to monitor and simulate urban climate from city down to building scale; and to integrate results directly into engineering and policy areas which transform urban infrastructure. The Core Project will be to build ACTUAL, requiring considerable development of instrumentation and data logging systems, with the goal of providing robust, representative climate data for London within 5 years. The research theme over the first five years is sustainable adaptation of buildings to a warmer London climate. Three interlinked Research Strands will exploit ACTUAL data within this theme: 1) improving urban climate simulation 2) assessing the effect of building layout on city ventilation and 3) developing tools to optimise urban renewable energy generation. The project brings together a diverse selection of engineers, meteorologists, local authority policy makers, and engineering consultants. Ensuring clear knowledge exchange between these areas is essential: so throughout the project a Virtual Urban Environment will be developed (City-VUE). This consists of integrated web-based and virtual educational activities to engage schools, the public, policy makers and engineers. ACTUAL and City-VUE will become key resources for engineers to underpin sustainable transformation of other aspects of urban infrastructure into the 21st century.