The project analyses the interactions between urban form, economic welfare, energy use by and emissions from households and firms. Increasing urban density and increasing city size tend to reduce households’ average energy consumption. However, increasing population density also tends to reduce local air quality. This trade-off as well as urban policies to stimulate the transition towards low carbon cities are subject of study. This is done by collecting data in four very different European cities – Amsterdam, Istanbul, Gothenburg and Barcelona – and by developing a spatial-economic equilibrium model that can be used for policy simulations. BREATHE engages policy makers and companies from the four cities.