I will present a study of the proportion of star-forming galaxies
at z=0 to 0.8 as a function of galaxy environment. This work is
based on 16 clusters, 10 groups and another 250 galaxies in poorer
groups and the field at z=0.4-0.8 from the ESO Distant Cluster Survey,
and the Sloan Digital Sky Survey as a local comparison.
Our high-z observations show that at z=0.4-0.8 the mass of the system
seems to largely determine the proportion of galaxies with ongoing
star formation.
The evolution of the relation between the star-forming fraction and the
system velocity dispersion suggests how galaxy star formation histories
may be closely related to the growth history of clusters and groups.
I will discuss the implications of these results for a possible
evolutionary scenario linking galaxy properties and environment.