Merger-remnant galaxies hosting dual supermassive black holes with kpc-scale separations are an expected consequence of galaxy mergers, and these dual supermassive black holes are useful as direct observational tracers of galaxy evolution. I will describe a systematic survey of dual supermassive black holes, which employs a combination of large spectroscopic surveys of galaxies, longslit spectroscopy, X-ray, and radio observations to identify dual supermassive black holes that power active galactic nuclei (AGN). I will present the initial results of this search, which is building up a large observational catalog of dual supermassive black holes. This catalog will enable new observational measurements of merger-driven AGN fueling, black hole mass growth via gas accretion during mergers, and the black hole merger rate of interest for future gravitational wave experiments.