--- Imre Bartos --- Multimessenger observations of binary neutron star merger GW170817 --- The recent discovery of gravitational wave GW170817 from two merging neutron stars by LIGO and Virgo was accompanied by detections across the electromagnetic spectrum from gamma rays to radio by dozens of observatories in space and around the globe. This watershed moment crowned decades of research and represents the beginning of multimessenger astrophysics with gravitational waves. I will discuss the electromagnetic observations in the aftermath of GW170817 and what we learned from them. ---