Abstract：One of the key open issue in galaxy formation and evolution is understanding the processes through which galaxies stopped forming stars and became passively evolving early-type objects. I will review current understanding of this issue, and present some ongoing work trying to improve our understanding via the study of plausible progenitors (galaxies on the     way to quenching) and of descendants (galaxies already quenched). The first generation of forming galaxy clusters at z~2 provide an excellent environment to study quenching in action and compare the possible role of different channels: removal of gas accretion flows, AGN feedback and mergers.