M91

M91 or M-91 may refer to:


 * Various iterations of the Carcano, an Italian rifle
 * M-91 (Michigan highway), a state highway in Michigan
 * M91 rocket launcher, a 115mm, 45-tube, trailer mount for the M55 rocket used by the United States Army and United States Marine Corps
 * McCarthy 91 function, a recursive function defined by the computer scientist John McCarthy as a test case for formal verification within computer science
 * Messier 91, a barred spiral galaxy about 63 million light-years away in the constellation Coma Berenices
 * Mosin Nagant Model 1891 Infantry Rifle, a Russian/Soviet rifle
 * Psihološko propagandni komplet M-91, the third studio album released in 1991 by Montenegrin-Serbian musician Rambo Amadeus
 * Zastava M91, a Serbian sniper rifle