During a major galaxy merger, two supermassive black holes will interact with a common environment as they sink to the center of the merging system. The black-hole pair will form a binary, eventually emitting the most intense gravitational radiation in the Universe until they coalesce. Standard cosmological growth models have predicted that up to 10% of galaxies could contain black-hole pairs at various stages of evolution, however the discovery of supermassive pairs in galaxies has been notoriously difficult. I will briefly review the astrophysical questions that the detection of supermassive pairs can address, and will detail efforts to detect electromagnetic emission, and gravitational radiation through pulsar timing, from dual supermassive black holes.