In this thesis we present the NOAO-XMM Cluster Survey (NXS). NXS has provided optical follow-up of X-ray cluster candidates serendipitously detected by the XMM Cluster Survey (XCS). We report details on the execution, data reduction and analysis of 154 wide-field MOSAIC images containing 630 XCS cluster candidates. We present a redshift algorithm, based on the ‘red-sequence technique', designed to confirm cluster identifications and extract photometric cluster redshifts from NXS data. This algorithm exploits the homogeneity of elliptical cluster galaxies to provide simultaneous redshift and optical richness estimates. In addition, we apply this redshift algorithm to the Sloan Digital Sky Survey public data releases SDSS DR7 and SDSS Stripe 82. The resulting catalogue of ~500 optically confirmed XCS clusters with red-sequence redshifts is presented, spanning the redshift range 0.1