A new research infrastructure to decipher the greenhouse gas balance of Europe and adjacent regions ICOS provides the long-term observations required to understand the present state and predict future behaviour of climate, the global carbon cycle and greenhouse gases emissions. Quick facts: ICOS is on the roadmap of the European Strategy Forum on Research Infrastructures. ICOS is in its Preparatory phase (2008-2013), funded by the European Commission under FP7. ICOS is a long term (20+ years) observatory. 17 European research laboratories participate to the Preparatory phase. 17 countries have national focal points to represent their scientific interests.