  The globally-averaged star formation rate in the Universe has been steadily
declining since at least z~1. This may be due either to very local processes
operating within the average galaxy, or to external, environmental effects.
Specifically, the build-up of structure may be responsible for terminating star
formation in some galaxies and thus decreasing the global average. We summarize
our previous and ongoing work to distinguish between these possibilities, by
determining the average star formation rate as a function of redshift and
environment, out to z=0.5.
