The emphasis of the group on observational cosmology has up to now mainly been on the study of clusters of galaxies at high and low redshifts, as well as their relation to active galactic nuclei (AGN). New directions also include modeling of early supernova activity, as well the use of supernovae as cosmological probes. In the latter field the group is collaborating with especially the cosmology group at the Dept. of Physics at Stockholm University.