ABSTRACT: NANOGrav has found evidence for the gravitational wave background from our pulsar timing array data. This Earth-moving new science is the result of fifteen years of work with contributions from over a hundred scientists and is consistent with other pulsar timing arrays. I will present our recent results and why we are confident in our results. I will discuss the interpretation of the background as due to a cosmic population of supermassive black hole binaries as well as other, more exotic ideas. I will present how our pulsar timing array data put constraints on the population of massive black holes and how we can improve these constraints with optical, infrared, and X-ray observations of galaxies and binary AGN.