The Red-Sequence Cluster Survey (RCS), consisting of 100 square degrees of imaging in the R_c and z' filters, is the largest moderately-deep imaging survey currently being carried out. The primary goal of the survey is to identify a large sample of galaxy clusters over a broad redshift and mass range, suitable for a number of studies focused in the areas of cosmology and galaxy evolution.

Critical to the success of the RCS has been the development of a new method for finding galaxy clusters. This method solves the problem of projection which has plagued previous deep optical cluster searches. A detailed justification for the method in the context of current knowledge of galaxy clusters is given, as well as a detailed description of the cluster finding algorithm. It is argued that this method, in conjunction with the imaging now available with large format cameras on moderate-sized telescopes, represents by far the most efficient method for detecting galaxy clusters to at least redshift one.

The survey strategy of the RCS is described, as is the data processing pipeline. A cluster catalog based on an analysis of first two complete survey patches (of twenty-two) is also given. This catalog is analysed using photometric methods to produce an estimate of the redshift evolution of the cluster mass spectrum, N(M,z). Combined with detailed modeling of the RCS cluster selection functions, and large scale n-body simulations from the literature, the measured N(M,z) shows that it is possible to measure cluster masses using only photometric data. Eventually, a similar analysis using the entire RCS sample will provide strong constraints on the matter density of the universe, [Omega]_M, and the normalisation of the cosmological power spectrum, [sigma]₈.

A detailed description of a newly discovered RCS cluster, RCS J02254-0002, is also given. RCS J0224-0002 is likely the single most striking strong-lensing cluster ever discovered, and some of the potential of such systems is described. A quick description of five other strong-lensing systems discovered in the RCS is provided; together these systems represent a major new sample of strong lensing clusters.

This thesis concludes with a summary of much of the other work being done with RCS data, and an indication of some of the followup currently planned or in progress. We also briefly describe plans for RCS-2, and argue that cluster surveys at z<1 using X-rays or the SZ effect are inefficient in comparison with optical surveys in light of these planned data.