On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a binary neutron star inspiral, known as GW170817. This event, detected with a combined signal-to-noise ratio of 32.4 and a false-alarm rate of less than one per 80,000 years, provided the first direct evidence of a link between neutron star mergers and short gamma-ray bursts. The source was localized to a sky region of 28 square degrees and had a luminosity distance of 40 ± 8 megaparsecs, making it the closest and most precisely localized gravitational-wave signal to date. The detection of a γ-ray burst, GRB 170817A, 1.7 seconds after the coalescence, confirmed the hypothesis that neutron star mergers produce short γ-ray bursts. Subsequent electromagnetic observations identified a counterpart in the galaxy NGC 4993, supporting the interpretation of GW170817 as a binary neutron star merger. The event's properties, including the masses of the merging neutron stars, were constrained using gravitational-wave data alone and in combination with electromagnetic observations. The detection of GW170817 marks the beginning of a new era in gravitational-wave astronomy, offering insights into astrophysics, dense matter, gravitation, and cosmology.On August 17, 2017, the Advanced LIGO and Advanced Virgo gravitational-wave detectors observed a binary neutron star inspiral, known as GW170817. This event, detected with a combined signal-to-noise ratio of 32.4 and a false-alarm rate of less than one per 80,000 years, provided the first direct evidence of a link between neutron star mergers and short gamma-ray bursts. The source was localized to a sky region of 28 square degrees and had a luminosity distance of 40 ± 8 megaparsecs, making it the closest and most precisely localized gravitational-wave signal to date. The detection of a γ-ray burst, GRB 170817A, 1.7 seconds after the coalescence, confirmed the hypothesis that neutron star mergers produce short γ-ray bursts. Subsequent electromagnetic observations identified a counterpart in the galaxy NGC 4993, supporting the interpretation of GW170817 as a binary neutron star merger. The event's properties, including the masses of the merging neutron stars, were constrained using gravitational-wave data alone and in combination with electromagnetic observations. The detection of GW170817 marks the beginning of a new era in gravitational-wave astronomy, offering insights into astrophysics, dense matter, gravitation, and cosmology.