Star clusters are becoming very useful probes in the studies of many topics in modern Astronomy. Actually, they are providing invaluable information about the origin, structure and star formation processes in extragalactic systems. Otherwise, most of our knowledge on how individual stars are formed is derived from the analysis of stellar clusters resolved into stars. In this contribution we review the main scientific objectives in this field, in the light of the first generation instruments for the Gran Telescopio Canarias.