Since the discovery in the early nineties of a missing terrestrial sink of carbon in the global carbon cycle (Tans et al. 1990), there was a tremendous effort of observation of the continental part of the carbon cycle. The most recent estimate of its magnitude proposed by the Global Carbon Project reaches 10.6 GtC CO2±2.9 in 2014. The continental ecosystems contribute to attenuate the anthropogenic greenhouse gases enhancement by 29%. This terrestrial sink is characterized by the large amplitude of its inter-annual variations and its ample uncertainty which makes it difficult to predict the future of the continental sink of carbon. Inversion of atmospheric concentrations in greenhouse gases (GHG) and their temporal variations combined with atmospheric transport model allows characterizing the GHG exchanges at the continental surface at typical scale of 10 to 100 km. Point measurements of the full GHG budget at half hourly resolution together with ancillary measurements on vegetation, management practices and soil permit to characterize the biogeochemical processes involved and their drivers. They are of utmost importance for understanding the GHG cycle and its sensitivity to environmental drivers on the long term. Thus far, however, the inhomogeneity of methods, protocols and instruments used across ground observation networks have limited strongly our capacity to detect and observe the effects of environmental changes that are assumed to provoke changes in the GHG cycle. Indeed, the rate of pollutants deposition (Ozone, Nitrogen compounds), solar dimming, climate change and CO2 concentration enhancement not mentioning the secondary drivers are not monitored with sufficient accuracy and neither co-located in a sufficient number of stations for attributing clearly changes in the GHG budget of the main terrestrial ecosystems. From this conclusion, the European research strategy implemented through the ESFRI roadmap was to build a new world class infrastructure having the capacity to coordinate and harmonise networks of ocean-, atmospheric- and ground-based stations equipped with identical instruments and operated according to the sale common protocols and standards, that is the ICOS infrastructure. This communication will present the ICOS ecosystem network of stations and the Ecosystem Thematic Centre which collects and processes the measurements that are being operated across the station network. It will give few examples of the data obtained so far and show how they are being used for establishing robust GHG budgets of different ecosystems and their sensitivity to the environment, management practices and interaction.