On August 17th, the gravitational wave detectors LIGO and Virgo observed for the first time the signature of a binary neutron star merger. Roughly two seconds later, the Fermi satellite detected a short gamma-ray burst whose location was consistent with the position of the gravitational wave source. These signals triggered an electromagnetic follow-up campaign by dozens of groups around the world, who quickly identified an electromagnetic counterpart, which was observed over the next several weeks at energies ranging from the x-ray to the radio. These observations allowed astronomers to construct a detailed picture of an event that had previously been studied only theoretically, and to test key theories about the nature of neutron star mergers. Among these is whether mergers are the astrophysical site of r-process nucleosynthesis, which produces roughly half of elements heavier than iron. I will give an overview of the electromagnetic observations of this system, with an emphasis on the optical and infrared emission (the "kilonova") powered by the radioactive decay of elements synthesized in the merger. I will outline how recent theoretical advances allowed us to interpret kilonova observations and decode signs of heavy element production.