Understanding the mechanisms responsible for transforming star forming galaxies into quiescent
system is currently one of the most interesting challenges in astrophysics.  I will discuss various observational results that suggest that different mechanisms are responsible for quenching star formation in different classes of galaxies. I will focus in particular on the observational evidence for “starvation” (in which the supply of gas supply to the galaxy is halted) and gas removal by massive outflows, and their relative role in different systems. Yet, additional phenomena must be invoked to also explain the “morphological” transformation of galaxies, and in particular the formation and growth of the spheroidal component of galaxies. The latter is generally associated with the effect of mergers or the so-called “compactation”. However, I will show observational evidence for a new phenomenon which may provide an alternative route for the formation of the spheroidal component of galaxies.