The gravitational-wave event GW170817, detected by the LIGO and Virgo detectors on August 17, 2017, marks the first observation of a binary neutron star (BNS) merger. This event was identified with a signal-to-noise ratio of 32.4 and a false-alarm rate of less than one per 8.0 × 10⁴ years. The component masses of the binary system were inferred to be between 0.86 and 2.26 solar masses, consistent with known neutron star masses. The total mass of the system was determined to be 2.74 ± 0.04 solar masses. The source was localized to a sky region of 28 deg² with a luminosity distance of 40 ± 8 Mpc, the closest and most precisely localized gravitational-wave signal ever detected. The event was associated with the gamma-ray burst GRB 170817A, detected 1.7 seconds after the merger, confirming the hypothesis of a neutron star merger and providing the first direct evidence of a link between BNS mergers and short gamma-ray bursts. Subsequent electromagnetic observations confirmed the event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insights into astrophysics, dense matter, gravity, and cosmology. The detection of GW170817 represents a significant milestone in gravitational-wave astronomy, opening a new era of discovery.The gravitational-wave event GW170817, detected by the LIGO and Virgo detectors on August 17, 2017, marks the first observation of a binary neutron star (BNS) merger. This event was identified with a signal-to-noise ratio of 32.4 and a false-alarm rate of less than one per 8.0 × 10⁴ years. The component masses of the binary system were inferred to be between 0.86 and 2.26 solar masses, consistent with known neutron star masses. The total mass of the system was determined to be 2.74 ± 0.04 solar masses. The source was localized to a sky region of 28 deg² with a luminosity distance of 40 ± 8 Mpc, the closest and most precisely localized gravitational-wave signal ever detected. The event was associated with the gamma-ray burst GRB 170817A, detected 1.7 seconds after the merger, confirming the hypothesis of a neutron star merger and providing the first direct evidence of a link between BNS mergers and short gamma-ray bursts. Subsequent electromagnetic observations confirmed the event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insights into astrophysics, dense matter, gravity, and cosmology. The detection of GW170817 represents a significant milestone in gravitational-wave astronomy, opening a new era of discovery.