A31

A31 or A-31 may refer to:
 * A31 cefiro, a series of cars by Nissan
 * A-31 Vengeance, an American dive bomber from the World War II era
 * Archambault A31, a French sailboat design
 * HLA-A31, a human serotype
 * Samsung Galaxy A31, a mid-range Android smartphone
 * IBM ThinkPad A31 laptop computer, produced circa 2002-2004

Roads

 * Highway 31 aka Autoroute 31
 * A31 motorway (Canada), a road in Quebec connecting Joliette and the A40
 * A31 road (England), a road connecting Guildford, Surrey and Bere Regis, Dorset
 * A31 motorway (France), a road connecting the Franco-Luxembourg border and Beaune
 * A31 motorway (Germany), a road connecting the coast of the North Sea near Emden to the Ruhr area
 * A31 road (Isle of Man), a road connecting Port St Mary with the Calf Sound
 * A31 motorway (Italy), a road connecting Piovene Rocchette and Albettone - Barbarano Vicentino
 * A31 motorway (Netherlands), a road connecting Harlingen and Leeuwarden
 * A31 motorway (Spain), a road connecting Madrid and Alicante
 * A31 highway (Sri Lanka), a road connecting Karaithivu and Ampara