The CNRM-CM5.1 global climate model is a new version of the CNRM-CM general circulation model developed by CNRM-GAME and Cerfacs to participate in the Coupled Model Intercomparison Project (CMIP5). The model includes the atmospheric model ARPEGE-Climat (v5.2), the ocean model NEMO (v3.2), the land surface scheme ISBA, and the sea ice model GELATO (v5), all coupled through the OASIS (v3) system. Key improvements over CMIP3 include increased horizontal resolution in both the atmosphere (from 2.8° to 1.4°) and ocean (from 2° to 1°), a revised dynamical core for the atmosphere, a new radiation scheme, and improved treatments of tropospheric and stratospheric aerosols. The land surface scheme ISBA has been externalized through the SURFEX platform, incorporating new developments such as sub-grid hydrology parameterization, a new freezing scheme, and a new bulk parameterization for ocean surface fluxes. The ocean model is based on the state-of-the-art NEMO version, which has significantly progressed since the OPA8.0 version used in CNRM-CM3. The coupling between components through OASIS has been improved to avoid energy loss and spurious drifts. These developments lead to a more realistic representation of the mean recent climate and a reduction of drifts in preindustrial integrations. The large-scale dynamics are generally improved in both the atmosphere and ocean, and the bias in mean surface temperature is clearly reduced. However, some flaws remain, such as significant precipitation and radiative biases in many regions, or a pronounced drift in three-dimensional salinity. The model is evaluated in terms of mean state, showing improved performance compared to CNRM-CM3, with reduced drifts in sea surface temperature and improved large-scale dynamics. The model is used for pre-industrial and historical simulations, with results compared to observations and reanalyses. The model's energy balance is assessed, showing a more realistic energy budget in CNRM-CM5.1 compared to CNRM-CM3. The ocean drifts are reduced in CNRM-CM5.1, with a weak positive trend in volumetric temperature and a dramatic increase in salinity drift, which is under investigation. The model's water conservation has been particularly checked, and the sea level rise estimate in PiCTL is still far from being negligible compared to the 20th century estimate. The model's performance is summarized, highlighting its strengths and weaknesses, and providing a background for interpreting results within a multi-model framework.The CNRM-CM5.1 global climate model is a new version of the CNRM-CM general circulation model developed by CNRM-GAME and Cerfacs to participate in the Coupled Model Intercomparison Project (CMIP5). The model includes the atmospheric model ARPEGE-Climat (v5.2), the ocean model NEMO (v3.2), the land surface scheme ISBA, and the sea ice model GELATO (v5), all coupled through the OASIS (v3) system. Key improvements over CMIP3 include increased horizontal resolution in both the atmosphere (from 2.8° to 1.4°) and ocean (from 2° to 1°), a revised dynamical core for the atmosphere, a new radiation scheme, and improved treatments of tropospheric and stratospheric aerosols. The land surface scheme ISBA has been externalized through the SURFEX platform, incorporating new developments such as sub-grid hydrology parameterization, a new freezing scheme, and a new bulk parameterization for ocean surface fluxes. The ocean model is based on the state-of-the-art NEMO version, which has significantly progressed since the OPA8.0 version used in CNRM-CM3. The coupling between components through OASIS has been improved to avoid energy loss and spurious drifts. These developments lead to a more realistic representation of the mean recent climate and a reduction of drifts in preindustrial integrations. The large-scale dynamics are generally improved in both the atmosphere and ocean, and the bias in mean surface temperature is clearly reduced. However, some flaws remain, such as significant precipitation and radiative biases in many regions, or a pronounced drift in three-dimensional salinity. The model is evaluated in terms of mean state, showing improved performance compared to CNRM-CM3, with reduced drifts in sea surface temperature and improved large-scale dynamics. The model is used for pre-industrial and historical simulations, with results compared to observations and reanalyses. The model's energy balance is assessed, showing a more realistic energy budget in CNRM-CM5.1 compared to CNRM-CM3. The ocean drifts are reduced in CNRM-CM5.1, with a weak positive trend in volumetric temperature and a dramatic increase in salinity drift, which is under investigation. The model's water conservation has been particularly checked, and the sea level rise estimate in PiCTL is still far from being negligible compared to the 20th century estimate. The model's performance is summarized, highlighting its strengths and weaknesses, and providing a background for interpreting results within a multi-model framework.