Xi Scorpii (ξ Sco, ξ Scorpii) is a star system in the constellation Scorpius. It was also 51 Lib.
The Xi Scorpii system consists of at least five stars in two groups separated by 4.67 arcminutes (or 0.08°) on the sky, corresponding to a distance of at least 8000 astronomical units (AU).
The brighter group contains Xi Scorpii A, B, and C. A and B are both yellow-white F-type stars. A is a slightly brighter and warmer magnitude +4.8 subgiant, while B is a magnitude +5.1 main sequence dwarf. They are separated by 0.76 arcseconds, or at least 21 AU, roughly a Sun–Uranus distance, and orbit around a common centre once every 46 years. The magnitude +7.6 Xi Scorpii C orbits this pair at ten times the distance, having a separation of 7.6 arcseconds.
The second group contains Xi Scorpii D and E. Both D and E are K-type stars, which are separated by 11.5 arcseconds, more than 320 AU.
Xi Scorpii also possesses a sixth component, the 11th magnitude Xi Scorpii F, located 81 arcseconds from D. It is not known to be gravitationally bound to the other five components.
Xi Scorpii was a latter designation of 51 Librae.