On Aug 17, 2017 the LIGO and Virgo detectors recorded gravitational waves (GW) consistent with coming from the coalescence of two neutron stars relatively nearby. About 2 seconds after the GW signal, a short pulse of gamma rays was independently detected by the Fermi satellite, from a direction similar to the GW trigger. Numerous groups started scanning the error lobes of the these detections (about 1% of the sky) with all available telescopes, and soon found a new optical transient with never-seen properties in a host galaxy at the correct distance. This includes the TAU group, using our network of 1m telescopes that is distributed around the globe. The transient was later detected all along the EM spectrum, from X-ray to radio. I will discuss the unambiguous association between the transient (called a kilonova or macronova) and the GW signal, its observed properties, the interpretation of the EM emission, and the prospect for future discoveries. I will also briefly discuss the sociology of this unprecedented event, in terms of the number of coordinated publications and the scale of community involvement.