| 1 | M | Montour R.R. Co. | 7/1930-10/1966 | | NAKINA |
| 2 | M | Montour R.R. | 8/1920-7/1923 | | NAKINA |
| 3 | M | Montour R.R. Co. | 4/38-10/66 | | NRHS |
| 4 | M | MONTOUR RR | | | PWRC |
| 5 | M | Magyar Államvasutak | | H | TRAFFIC |
| 6 | M&BT | Marianna & Blountstown R.R. | 7/1923-1/1950 | | NAKINA |
| 7 | M&BT | Marianna & Blountstown R.R. | Apr-38 | | NRHS |
| 8 | M&BT | MARIANNA & BLOUNTSTOWN RAILROAD | | | PWRC |
| 9 | M&K | Morgantown & Kingwood R.R. (Baltimore & Ohio R.R.) | 7/1923 | | NAKINA |
| 10 | M&K | Morgantown & Kingwood R.R. | 8/1920 | | NAKINA |
| 11 | M&K | BALTIMORE & OHIO RAILROAD [MORGANTOWN & KINGWOOD RAILROAD] | | | PWRC |
| 12 | M&LS | Manistique & Lake Superior R.R. | 7/1930-7/1936 | | NAKINA |
| 13 | M&LS | MANISTIQUE & LAKE SUPERIOR RAILROAD | | | PWRC |
| 14 | M&M | Meridian and Memphis Ry. Co. (Gulf, Mobile and Northern R.R. Co.) | 8/1920-7/1923 | | NAKINA |
| 15 | M&M | GULF, MOBILE & NORTHERN RAILROAD CO. [MERIDIAN & MEMPHIS RWY. CO.] | | | PWRC |
| 16 | M&NA | Missouri & Northern Arkansas Ry. Co. | 7/1923-4/1938 | | NAKINA |
| 17 | M&NA | Missouri & Northern Arkansas R.R. | 8/1920 | | NAKINA |
| 18 | M&NA | Missouri & Northern Arkansas Ry. Co. | Apr-38 | | NRHS |
| 19 | M&NA | MISSOURI & NORTH ARKANSAS RWY. CO. | | | PWRC |
| 20 | M&NE | Manistee & Northeastern Ry. Co. | 7/1930-7/1954 | | NAKINA |
| 21 | M&NE | Manistee & Northeastern R.R. Co. | 8/1920-7/1923 | | NAKINA |
| 22 | M&NE | Manistee & Northeastern Ry. Co. | 4/38-1/52 | | NRHS |
| 23 | M&NE | MANISTEE & NORTHEASTERN RY. CO. | | | PWRC |
| 24 | M&PA | Maryland & Pennsylvania R.R. Co. | 4/1970 | | NAKINA |
| 25 | M&PA | Maryland & Pennsylvania R.R. (Co.) | 8/1920-10/1966 | | NAKINA |
| 26 | M&PA | Maryland & Pennsylvania R.R. | 4/38-10/66 | | NRHS |
| 27 | M&PA | Maryland & Pennsylvania R.R. Co. | Apr-70 | | NRHS |
| 28 | M&PA | MARYLAND & PENNSYLVANIA RAILROAD CO. | | | PWRC |
| 29 | M&RR | Minneapolis & Rainy River Ry. Co. | 8/1920-7/1932 | | NAKINA |
| 30 | M&RR | MINNEAPOLIS & RAINY RIVER RWY. CO. | | | PWRC |
| 31 | M&STL | MINNEAPOLIS & ST. LOUIS | | | PWRC |
| 32 | M&U | Middletown & Unionville R.R. | 8/1920-7/1936; 1/1941-1/1946 | | NAKINA |
| 33 | M&U | MIDDLETOWN & UNIONVILLE RAILROAD | | | PWRC |
| 34 | M&W | Morgantown & Wheeling Ry. Co. | 7/1923 | | NAKINA |
| 35 | M&W | MORGANTOWN & WHEELING RWY. CO. | | | PWRC |
| 36 | M&WR | Montpelier & Wells River R.R. | 7/1930-1/1941 | | NAKINA |
| 37 | M&WR | Montpelier & Wells River R.R. (Boston & Maine R.R.) | 8/1920-7/1923 | | NAKINA |
| 38 | M&WR | Montpelier and Wells River R.R. | Apr-38 | | NRHS |
| 39 | M&WR | BOSTON & MAINE RAILROAD [MOHTPELIER & WELLS RIVER RAILROAD] | | | PWRC |
| 40 | M-K-T | Missouri-Kansas-Texas R.R. Co. | 4/1938 | | NAKINA |
| 41 | M-K-T | Missouri-Kansas-Texas R.R. Co. (M.-K.-T. Lines) | 7/1923-7/1936 | | NAKINA |
| 42 | M-K-T | Missouri-Kansas-Texas R.R. Co. | Apr-38 | | NRHS |
| 43 | M-K-T | MISSOURI, KANSAS & TEXAS RWY. (M.K. & T. LINES) | | | PWRC |
| 44 | M0 | Aero Mongolia | ICAO: MNG, Callsign: Aero Mongolia, IATA Prefix: 970, | MGL | AVCODES |
| 45 | M1 | Zambezi Transfer Services CC dba Air Reps | Designator M1 recalled by IATA. Computer Reservations Systems (CRS) | ZA | AVCODES |
| 46 | M2 | Mario's Air, Inc. | Designator M2* recalled by IATA | USA | AVCODES |
| 47 | M2 | Mahfooz Aviation (Gambia) Ltd. | ICAO: MZS, Callsign: Mahfooz, Name changed from Mahfooz Aviation G Limited | SA | AVCODES |
| 48 | M2 | Mahfooz Aviation G. Limited | ICAO: MZS, Callsign: Mahfooz, Name changed to Mahfooz Aviation (Gambia) Ltd. | SA | AVCODES |
| 49 | M2 | Air Manas d/b/a Air Manas Ltd. Air Company | ICAO: MBB, Callsign: Air Manas, Founded in 2006. IATA designator changed to ZM | KS | AVCODES |
| 50 | M2 | MHS Aviation GmbH | ICAO: MHV, Callsign: Snowcap, | D | AVCODES |
| 51 | M2 | Sunrise Airlines, Inc. d/b/a Millon Express | ICAO: MXS, Callsign: Millon Express, IATA Prefix: 592, | USA | AVCODES |
| 52 | M3 | North Flying A/S | ICAO: NFA, Callsign: North Flying, Designator 6Z* recalled by IATA | DK | AVCODES |
| 53 | M3 | Air Service | ICAO: SPJ, Callsign: Air Skopje, | MK | AVCODES |
| 54 | M3 | Westjet Airlines Ltd. | ICAO: WJA, Callsign: Westjet, IATA designator changed to WS | CDN | AVCODES |
| 55 | M3 | Filder Air Service Airlines | ICAO: NRX, Callsign: Noris, Merged into European Air Express | D | AVCODES |
| 56 | M3 | European Air Express | ICAO: NRX, Callsign: Noris, ICAO designator changed to EAE, Formely Filder Air Servic Airlines | D | AVCODES |
| 57 | M3 | European Air Express | ICAO: NRX, Callsign: Noris, IATA designator changed to 7Y*. ICAO designator changed to EAE. Formely Filder Air Servic Airlines | D | AVCODES |
| 58 | M4 | Avioimpex A.D.p.o. | ICAO: AXX, Callsign: Impex, IATA Prefix: 743, Founded in 1992. Ceased operations in September 2002. Name changed from Interimpex - Avioimpex | MK | AVCODES |
| 59 | M4 | Nayzak Air Transport Company | ICAO: NZA, IATA Prefix: 728, Designator M4 reinstated by IATA | LAR | AVCODES |
| 60 | M4 | Polar Airlines de Mexico, S.A. de C.V. | ICAO: PMO, Ceased Operations | MEX | AVCODES |
| 61 | M4 | Smart Aviation Company | ICAO: SME, Callsign: Smart Aviation, Designator M4 recalled by IATA | ET | AVCODES |
| 62 | M4 | Mistral Air S.r.l. | ICAO: MSA, Callsign: Mistral Wings, Name changed to Poste Air Cargo S.r.l. October 2019. IATA Designator changed from 7M. ICAO callsign changed from Aiemerci | I | AVCODES |
| 63 | M4 | Poste Air Cargo S.r.l. | ICAO: MSA, Callsign: Mistral Wings, IATA Prefix: 408, Name changed from Mistral Air S.r.l. October 2019. IATA Designator changed from 7M. ICAO callsign changed from Aiemerci | I | AVCODES |
| 64 | M5 | Kenmore Air | | USA | AVCODES |
| 65 | M5 | Kenmore Air Harbor, Inc. t/a Kenmore Air | ICAO: KEN, Callsign: Kenmore, | USA | AVCODES |
| 66 | M6 | Amerijet International, Inc. | ICAO: AJT, Callsign: Amerijet, IATA Prefix: 810, | USA | AVCODES |
| 67 | M6 | Chalair | ICAO: CLG, Callsign: Challair, Designator M6* recalled by IATA | F | AVCODES |
| 68 | M7 | Superior Aviation Services Ltd. | ICAO: SUK, Callsign: Skycargo, Designator M& recalled by IATA | EAK | AVCODES |
| 69 | M7 | Tropical Airways D'Haiti | ICAO: TBG, Designator M7* reinstated by IATA | RH | AVCODES |
| 70 | M7 | Marsland Aviation | ICAO: MSL, Callsign: Marslandair, Ceased operations during 2013. | SUD | AVCODES |
| 71 | M7 | Mountain Air Express, Inc. | ICAO: PKP, Callsign: Pikes Peak, Designator M7 recalled by IATA | USA | AVCODES |
| 72 | M7 | Aerotransportes Mas de Carga, S.A. de C.V. t/a MasAir | ICAO: MAA, Callsign: MAS Carga, IATA Prefix: 865, Name changed to Aerotransportes Mas de Carga, S.A. de C.V. d/b/a LATAM Cargo Mexico w.e.f. 05/05/2016. IATA designator changed from MY. Designator MY reinstated by IATA | MEX | AVCODES |
| 73 | M7 | Aerotransportes Mas de Carga, S.A. de C.V. d/b/a LATAM Cargo Mexico | ICAO: MAA, Callsign: MAS Carga, IATA Prefix: 865, Name reverted to Aerotransportes Mas de Carga, S.A. de C.V. t/a MasAir w.e.f. 01/12/2018. Name changed from Aerotransportes Mas de Carga, S.A. de C.V. t/a MasAir w.e.f. 05/05/2016. IATA designator changed from MY. Designator MY reinstated by IATA | MEX | AVCODES |
| 74 | M7 | Aerotransportes Mas de Carga, S.A. de C.V. t/a MasAir | ICAO: MAA, Callsign: MAS Carga, IATA Prefix: 865, Name changed from Aerotransportes Mas de Carga, S.A. de C.V. d/b/a LATAM Cargo Mexico w.e.f. 01/12/2018. IATA designator changed from MY. Designator MY reinstated by IATA | MEX | AVCODES |
| 75 | M8 | Moscow Airways | ICAO: MSC, | RUS | AVCODES |
| 76 | M8 | Med Airlines S.p.A. | ICAO: MDS, Callsign: Mizar, Ceased operations on 15 March 2001. | I | AVCODES |
| 77 | M8 | Mekong Airlines Co. Ltd. | ICAO: MKN, Callsign: Mekong Airlines, Ceased Operations in October 2003. Name changed from Yana Airlines Co. Ltd. | K | AVCODES |
| 78 | M8 | Maldives International Airlines | Callsign: Mike Dravo, | MV | AVCODES |
| 79 | M8 | Airmax S.A. | Designator M8* recalled by IATA. | PE | AVCODES |
| 80 | M8 | Transnusa Aviation Mandiri, PT. | ICAO: TNU, Callsign: Transnusa, | RI | AVCODES |
| 81 | M8 | Magnum Air, Inc. d/b/a Skyjet | ICAO: MSJ, Callsign: Magnum Air, Founded in 2005. Commenced operations on 14 December 2012. | RP | AVCODES |
| 82 | M9 | Motor-Sich, JSC | ICAO: MSI, Callsign: Motor Sich, IATA Prefix: 011, | UA | AVCODES |
| 83 | MA | MALEV Hungarian Airlines Public Limited Company (MALEV p.l.c.) | ICAO: MAH, Callsign: Malev, IATA Prefix: 182, Name changed to MALEV Hungarian Airlines Limited | H | AVCODES |
| 84 | MA | MAE Aircraft Management WLL | ICAO: MEN, Callsign: Rahal, IATA Prefix: 723, | BRN | AVCODES |
| 85 | MA | MALEV Hungarian Airlines Limited | ICAO: MAH, Callsign: Malev, IATA Prefix: 182, Ceased operations on 03 February 2012 and declared bankrupt on 14 February 2012. Name changed from MALEV Hungarian Airlines Public Limited Company (MALEV p.l.c.) | H | AVCODES |
| 86 | MA | Elitavia Malta Ltd | ICAO: EAU, Callsign: Elite, | M | AVCODES |
| 87 | MA | Missouri and Arkansas Ry. | 1/1941-7/1954 | | NAKINA |
| 88 | MA | Missouri and Arkansas Ry. | Jan-52 | | NRHS |
| 89 | MA | MISSOURI & ARKANSAS RWY. | | | PWRC |
| 90 | MA | MID AMERICA CHARTER LINES INC | | | SCAC4 |
| 91 | MA&C | Minneapolis, Anoka and Cuyuna Range R.R. Co. | 7/1932-4/1938 | | NAKINA |
| 92 | MA&C | Minneapolis, Anoka and Cuyuna Range Ry. Co. | 7/1930 | | NAKINA |
| 93 | MA&C | Minneapolis, Anoka and Cuyuna Range Ry. | 7/1923 | | NAKINA |
| 94 | MA&C | Minneapolis, Anoka and Cuyuna Range R.R. Co. | Apr-38 | | NRHS |
| 95 | MA&C | MINNEAPOLIS, ANOKA & CUYUNA RANGE RAILROAD CO. | | | PWRC |
| 96 | MA&PA | MARYLAND & PENNSYLVANIA | | | PWRC |
| 97 | MA&S | Maxton, Alma & Southbound R.R. Co. | 8/1920-7/1923 | | NAKINA |
| 98 | MA&S | MAXTON, ALMA & SOUTHBOUND RAILROAD CO. | | | PWRC |
| 99 | MAA | Aerotransportes Mas de Carga, S.A. de C.V. t/a MasAir | IATA: MY, Callsign: MAS Carga, IATA Prefix: 865, Founded in 1992. Commenced operations on 01/04/1992. IATA designator changed to M7. Designator MY reinstated by IATA | MEX | AVCODES |
| 100 | MAA | Aerotransportes Mas de Carga, S.A. de C.V. t/a MasAir | IATA: M7, Callsign: MAS Carga, IATA Prefix: 865, Name changed to Aerotransportes Mas de Carga, S.A. de C.V. d/b/a LATAM Cargo Mexico w.e.f. 05/05/2016. IATA designator changed from MY. Designator MY reinstated by IATA | MEX | AVCODES |
