Exoplanets increase significantly the parameter space span by solar-system planets in terms of mass, radius, composition, irradiation and internal heat flow. They are a fantastic opportunity to test the universality of mechanisms that are proposed as ad-hoc explanations to the specificities of our solar-system planets. Through remote sensing of exoplanet atmospheres we have detected many different molecular and atomic species. Quantifying their abundances is, however, a harder task that should become easier in the coming decade with the arrival of a new generation of ground and space based telescope. I will review what robust trends can be picked-up from current observations of exoplanets atmospheres and discuss to which degree they are influenced by the internal properties of these objects. Finally, I’ll explain how future telescopes should be able obtain similar information for cooler and/or smaller objects that will be much closer in parameter space to Jupiter and Saturn than from currently characterised exoplanets.