  The color-magnitude relation (CMR) of early-type galaxies in clusters
provides a powerful tool for finding clusters and determining photometric
redshifts for clusters using two-filter imaging data. We demonstrate the high
accuracy of photometric redshifts attainable using the CMR by applying the
technique to a sample of 45 Abell clusters with known redshifts. Furthermore,
by using the red sequence of galaxies from the CMR, we have developed an
extremely efficient technique for detecting clusters and groups of galaxies. We
demonstrate this using both observed photometric catalogs with redshifts (from
the CNOC2 Survey) and simulations.
