Compact galaxy groups are high-density, low-velocity dispersion environments, and as such they are ideal laboratories for studying galaxy transformations induced by gravitational interactions and associated phenomena, like the star-formation enhancement and the nuclear activity. I will present some results of detailed analyses of a few examples of dense galaxy systems spanning a wide range in evolutionary phases. On the basis of both observations and models, I will discuss in particular the star formation properties of these groups and the effects of the interactions on their member galaxies, as clues to their evolutionary status.