M31

M31 may refer to:

Roadways

 * M31 motorway, a planned but unbuilt motorway in England
 * M-31 (Michigan highway), a former state highway in Michigan
 * Hume Highway in Australia, designated "M31"
 * M31 motorway (Hungary), a short motorway section near Budapest, Hungary
 * M31 (Cape Town), a Metropolitan Route in Cape Town, South Africa
 * M31 (Johannesburg), a Metropolitan Route in Johannesburg, South Africa
 * M31 (Pretoria), a Metropolitan Route in Pretoria, South Africa
 * M31 (Durban), a Metropolitan Route in Durban, South Africa

Military

 * Suomi M-31 SMG, a Finnish WWII-era submachine gun
 * M31 HEAT rifle grenade
 * M31 Recovery Vehicle based on the M3 Lee tank
 * M31 rocket, an alternate designation for the MGR-1 Honest John, a United States military rocket
 * M31 (missile), for a multiple-launch rocket system (MLRS)
 * M31 is the pennant number for HMS Cattistock, a Hunt-class mine countermeasures vessel

Other

 * M31 = 0x7FFFFFFF = 2147483647, the eighth Mersenne prime number
 * M31 (New York City bus), a New York City Bus route in Manhattan
 * M31: A Family Romance, a novel by writer Stephen Wright
 * Messier 31 (M31), a spiral galaxy also called the Andromeda Galaxy
 * Samsung Galaxy M31, an Android based smartphone