At the last General Assembly of the IAU, in Patras, we had a Joint Discussion about the evolution in old stellar populations in galaxies. Then, as will be the case today, the great emphasis was placed on star formation and stellar evolution, on luminosity functions and mass functions. Today our theme does not include the word stellar. This is intentional. The young populations we are going to discuss will to a large extent concern the gaseous component in galaxies. The gas and the dust may from some points of view be considered old. However, when it takes part in star formation we discuss it as a part of the young population.