The EMC3 (Etude et Modélisation du climat et du changement climatique) team has been developing the General Circulation Model (GCM) LMDz since its origin (1990s) and became a community code. This model is the atmospheric component of the IPSL Earth System model (one of the two French climate models). Within the framework of the IPSL’s Climate Modelling Centre, this model has several hundred users in France and abroad, and since 2003 has been participating in the international CMIP project for the intercomparison of climate models within the World Climate Research Programme (WCRP) of the World Meteorological Organisation (WMO). At the same time, using LMDz, other models and observations, the team is studying the physical processes that govern climate and climate change. It plays a leading role in many of the WCRP’s international activities, in the preparation of IPCC reports and in other expert work on climate change. The team has strong links with mesoscale modelling, modelling of global atmospheres, continental surfaces and observations (analysis of data from space or instrumented sites such as SIRTA, involvement in field campaigns). These collaborations are an asset for the study of critical climate processes (e.g. clouds, convection, aerosols, surface hydrology) and the development of original parameterisations for large-scale models.