This paper presents the IPSL-CM5 Earth System Model (ESM), developed as part of the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). The model includes an interactive carbon cycle, tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. It can be used in various configurations with different boundary conditions and complexities. The paper outlines the model components and their couplings, and explains how they were used to simulate historical climate changes over the past 150 years and future climate change scenarios. The results suggest that the magnitude of global warming projections depends on the socio-economic scenario considered, and that aggressive mitigation policies can limit global warming to about two degrees Celsius. The paper also highlights the importance of atmospheric physical processes in influencing simulated climate variability and the magnitude and pattern of projected climate changes.This paper presents the IPSL-CM5 Earth System Model (ESM), developed as part of the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). The model includes an interactive carbon cycle, tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. It can be used in various configurations with different boundary conditions and complexities. The paper outlines the model components and their couplings, and explains how they were used to simulate historical climate changes over the past 150 years and future climate change scenarios. The results suggest that the magnitude of global warming projections depends on the socio-economic scenario considered, and that aggressive mitigation policies can limit global warming to about two degrees Celsius. The paper also highlights the importance of atmospheric physical processes in influencing simulated climate variability and the magnitude and pattern of projected climate changes.