Under the European GMES (Global Monitoring for Environment and Security), the European Union is currently developing a pilot project (MACC: Monitoring Atmospheric Composition and Climate) for global and regional atmospheric services. The project has started to implement and improve systems that monitor the global distributions of atmospheric constituents important for climate, and that monitor and forecast constituents affecting air quality and surface solar radiation. The purpose of the session is to review the state of the art in the development of atmospheric services, in modelling data-assimilation and inversion, using both satellite and in-situ data, in the domains of greenhouse gases, reactive gases, aerosols and regional air quality.