31 may refer to:
31 (number), the natural number following 30 and preceding 32
Years 31 BC AD 31 1931 2031
Music Thirty One (Jana Kramer album), 2015 Thirty One (Jarryd James album), 2015 "Thirty One", a song by Karma to Burn from the album Wild, Wonderful Purgatory, 1999
Science Gallium, a post-transition metal in the periodic table 31 Euphrosyne, an asteroid in the asteroid belt (31) Euphrosyne I, a satellite of 31 Euphrosyne
Film and television 31 (film), a 2016 horror film 31 (Kazakhstan), a television channel 31 Digital, an Australian video on demand service
Transportation 31st (CTA station), a rapid transit station in Chicago Route 31 (MBTA), a bus route in Boston, Massachusetts 31 (RIPTA), a bus route in Rhode Island
Other uses Thirty-one (card game) Baskin-Robbins, a U.S. international ice cream parlor chain with the slogan, "31 flavors" The international calling code for the Netherlands
See also 31st (disambiguation)
Channel 31 (disambiguation) Section 31 (disambiguation) List of highways numbered 31