ECLIPSE aims to develop and assess effective emission abatement strategies for short-lived climate agents in order to provide sound scientific advice on how to mitigate climate change while improving the quality of air. Current climate policy does not consider a range of short-lived gases and aerosols, and their precursors (including nitrogen oxides, volatile organic compounds, sulphate, and black carbon). These nevertheless make a significant contribution to climate change and directly influence air quality.There are fundamental scientific uncertainties in characterizing both the climate and air quality impacts of short-lived species and many aspects (for example, the regional dependence) are quite distinct to those for the longer-lived climate gases already included in the Kyoto Protocol.ECLIPSE will bring together 11 institutes with established and complementary expertise for a closely co-ordinated 3 year programme. It will build on existing knowledge and use state-of-the-art chemistry and climate models to (i) improve understanding of key atmospheric processes (including the impact of short-lived species on cloud properties) and characterize existing uncertainties; (ii) evaluate model simulations of short-lived species and their long-range transport using ground-based and satellite observations; (iii) perform case studies on key source and receptor regions (focused on Southeastern Europe, China and the Arctic); (iv) quantify the radiative forcing and climate response due to short-lived species, incorporating the dependence on where the species are emitted; (v) refine the calculation of climate metrics, and develop novel metrics which, for example, consider rate of climate warming and go beyond using global-mean quantities; (vi) clarify possible win-win and trade-off situations between climate policy and air quality policy; (vii) identify a set of concrete cost-effective abatement measures of short-lived species with large co-benefits.