I illustrate recent observational evidence for the existence of a link between properties of galaxies in groups/clusters and the assembly history of their parent halo. This evidence stems particularly from multi-wavelength studies of the galaxy population and substructure in massive clusters up to z=0.3, the fraction of star-forming galaxies in groups at redshifts 0.3--0.5, and the stellar and baryon mass fractions in clusters/groups up to z=1. Finally, I discuss some future investigations based on the reported findings, such as the use of fossil groups as laboratories for sharpened tests on LCDM universes and baryon physics.