Planets are born in disks composed of gas and dust surrounding new born stars, called protoplanetary disks. Giant gaseous planets such as Jupiter and Saturn are thought to have formed while there was still a lot of gas in these disks. Consequently, it should exist a link between the composition of the giants and the composition of the primordial gas in which they are born.
I will talk about the main processes involved in planet formation and how they are linked to their birth environment. I will present some recent results linking the observed composition of exoplanets to our planet formation models. To finish, we can discuss about how the JWST may help us understand better how planetary atmospheres evolve.