The last twenty five years have witnessed an exceptionally fast development in the field of exoplanets. About 4000 exoplanets have been detected so far. While the detection of exoplanets will remain an important field of activity, another chapter is in rapid development: the characterization of their atmosphere. The interest in observing exoplanet atmospheres goes well beyond the study of atmospheres very different from those found in the Solar system. Indeed, the molecular composition of giant exoplanet atmospheres can trace the planet's formation and evolution; the atmosphere of rocky exoplanets can host bio-signature gases,… In this seminar, I will draw the state of the art and the perspectives in the domain. Thanks to its large collective area and its suite of instruments covering a wide range of wavelengths (0.6-28 microns), the James Webb Space Telescope (JWST) will be THE key facilities in the 20’s to study the atmosphere of exoplanets. In 2028, the M4 ESA mission, ARIEL, entirely devoted to the study of exoplanet atmospheres, will be launched and will allow statistical studies; indeed, 1000 extra-solar planet atmospheres will be observed. The field has to face many challenges in data reduction, in modelling (1D, 2D, 3D), in retrieval techniques; the H2020 ExoplANETS-A project to tackle those will be presented.