| M | Marquess; Middle; Monsieur |
| m | married |
| MA | Master of Arts; Military Assistant; Massachusetts |
| MAA | Manufacturers' Agents Association of Great Britain |
| MACE | Member, Australian College of Education; Member, Association of Conference Executives |
| MACI | Member, American Concrete Institute |
| MAE | Member, Academia Europaea |
| MAFF | Ministry of Agriculture, Fisheries and Food |
| MAI | Magister in Arte Ingenlaria (Master of Engineering) |
| Maj | Major |
| Man | Manitoba |
| MAO | Master of Obstetric Art |
| MAOT | Member, Association of Occupational Therapists |
| MASc | Master of Applied Science |
| MASCE | Member, American Society of Civil Engineers |
| Mass | Massachusetts |
| Math | Mathematics; Mathematical |
| MATSA | Managerial Administrative Technical Staff Association |
| MB | Bachelor of Medicine; Medal of Bravery (Canada) |
| MBA | Master of Business Administration |
| MBC | Metropolitan/Municipal Borough Council |
| MBCS | Member, British Computer Society |
| MBE | Member, Order of the British Empire |
| MBFR | Mutual and Balanced Force Reductions (negotiations) |
| MBIM | Member, British Institute of Management |
| MBOU | Member, British Ornithologists' Union |
| MBritIRE | Member, British Institution of Radio Engineers |
| MBS | Member, Building Societies Institute |
| MC | Military Cross; Missionaries of Charity |
| MCB | Master in Clinical Biochemistry |
| MCC | Marylebone Cricket Club; Metropolitan County Council |
| MCh/MChir | Master of Surgery |
| MCIH | Member, Chartered Institute of Housing |
| MCIM | Member, Chartered Institute of Marketing |
| MCIOB | Member, Chartered Institute of Building |
| MCIT | Member, Chartered Institute of Transport |
| MCIWEM | Member, Chartered Institution of Water and Environmental Management |
| MCom | Master of Commerce |
| MConsE | Member, Association of Consulting Engineers |
| MCP | Member of Colonial Parliament; Master of City Planning (US) |
| MCS | Madras Civil Service; Malayan Civil Service |
| MCSD | Member, Chartered Society of Designers |
| MCSP | Member, Chartered Society of Physiotherapy |
| MCST | Member, College of Speech Therapists |
| md | managing director |
| MDC | Metropolitan District Council |
| MDS | Master of Dental Surgery |
| ME | Mining Engineer; Middle East; Master of Engineering; Maine |
| MEAF | Middle East Air Force |
| MEC | Member of Executive Council; Middle East Command |
| Mech | Mechanics; Mechanical |
| MEd | Master of Education |
| MEF | Middle East Force |
| MEIC | Member, Engineering Institute of Canada |
| MELF | Middle East Land Forces |
| Memb | Member |
| Meml | Memorial |
| Mencap | Royal Society for Mentally Handicapped Children and Adults |
| MEng | Master of Engineering |
| MEP | Member of the European Parliament |
| MFA | Master of Fine Arts |
| MFCM | Member, Faculty of Community Medicine |
| MFH | Master of Fox Hounds |
| MFHom | Member, Faculty of Homeopathy |
| MFOM | Member, Faculty of Occupational Medicine |
| MFPHM | Member, Faculty of Public Health Medicine |
| mfr | Manufacturers; manufacturer |
| MG | Machine Gun |
| MGC | Machine Gun Corps |
| MGM | Metro-Goldwyn-Mayer |
| Mgr | Manager,-s; Monsignor |
| MI | Military Intelligence; Michigan |
| MIAgrE | Member, Institution of Agricultural Engineers |
| MIAM | Member, Institute of Administrative Management |
| MIBiol | Member, Institute of Biology |
| MICE | Member, Institution of Civil Engineers |
| MICEI | member, institution of civil Engineers of Ireland |
| MICFor | Member, Institute of Chartered Foresters |
| Mich | Michigan |
| MIChemE | Member, Institution of Chemical Engineers |
| MICS | Member; institute of Chartered Shipbrokers |
| Middx | Middlesex |
| MIE | Member Institution of Engineers |
| MIE(Aust) | Member, Institution of Engineers, Australia |
| MIED | Member, Institution of Engineering Designers |
| MIEE | Member, Institution of Electrical Engineers |
| MIEI | Member, Institution of Engineering Inspection |
| MIEnvSc | Member, Institute of Environmental Science |
| MIERE | Member, Institution of Electronic and Radio Engineers |
| MIES | Member, Institution of Engineers and Shipbuilders, Scotland |
| MIHT | Member, Institution of Highways and Transportation |
| Mil | Military; Militia |
| MILocoE | Member, Institution of Locomotive Engineers |
| MIM | Member, Institute of Metals (formerly Institution of Metallurgists) |
| MIMarE | Member, Institute of Marine Engineers |
| MIMC | Member, Institute of Management Consultants |
| MIMechE | Member, Institution of Mechanical Engineers |
| MIMgt | Member, Institute of Management |
| MIMinE | Member, Institute of Mining Engineers |
| MIMM | Member, Institution of Mining and Metallurgy |
| Min | Minister; Ministry |
| Minn | Minnesota |
| MInstAM | Member, Institute of Administrative Management |
| MInstCE | Member, Institution of Civil Engineers |
| MInstD | Member, Institute of Directors |
| MInstMC | Member, Institute of Measurement and Control |
| MInstPet | Member, Institute of Petroleum |
| MInstT | Member, Institute of Transport |
| MIOM | Member, Institute of Office Management |
| MIOSH | Member, Institution of Occupational Safety and Health |
| MIPA | Member, Institute of Practitioners in Advertising |
| MIPD | Member, Institute of Personnel and Development |
| MIPM | Member, Institute of Personnel Management |
| MIPR | Member, Institute of Public Relations |
| MIProdE | Member, Institution of Production Engineers |
| MIQA | Member, Institute of Quality Assurance |
| MIStructE | Member, Institution of Structural Engineers |
| MIT | Massachusetts Institute of Technology |
| MIWE | Member, Institution of Water Engineers |
| MIWEM | Member, Institution of Water and Environmental Management |
| MJI | Member, Institute of Journalists |
| MLA | Member of Legislative Assembly; Modern Language Association; Master in Landscape Architecture |
| MLC | Member of Legislative Council |
| MLitt | Master of Letters |
| MM | Military Medal; Merchant Marine |
| Mme | Madame |
| MMM | Member, Order of Military Merit (Canada) |
| MN | Merchant Navy; Minnesota |
| MNI | Member, Nautical Institute |
| MO | Medical Officer; Military Operations; Missouri |
| MOD | Ministry of Defence |
| MOH | Medical Officer(s) of Health |
| MOI | Ministry of Information |
| Mon | Monmouthshire |
| Most Rev | Most Reverend |
| MP | Member of Parliament |
| MPH | Master of Public Health |
| MPS | Member, Pharmaceutical Society |
| MR | Master of the Rolls; Municipal Reform |
| MRAC | Member, Royal Architectural Institute of Canada; Royal Agricultural College |
| MRACP | Member, Royal Australasian College of Physicians |
| MRAeS | Member, Royal Aeronautical Society |
| MRAIC | Member, Royal Architectural Institute of Canada |
| MRAS | Member, Royal Asiatic Society |
| MRC | Medical Research Council |
| MRCGP | Member, Royal College of General Practitioners |
| MRCOG | Member, Royal College of Obstetricians and Gynaecologists |
| MRCP | Member, Royal College of Physicians, London |
| MRCPath | Member, Royal College of Pathologists |
| MRCPE | Member, Royal College of Physicians, Edinburgh |
| MRCPI | Member, Royal College of Physicians of Ireland |
| MRCS | Member, Royal College of Surgeons of England |
| MRCSE | Member, Royal College of Surgeons of Edinburgh |
| MRCVS | Member, Royal College of Veterinary Surgeons |
| MRI | Member, Royal Institution |
| MRIA | Member, Royal Irish Academy |
| MRIN | Member, Royal Institute of Navigation |
| MRINA | Member, Royal Institution of Naval Architects |
| MRO | Member, Register of Osteopaths |
| MRPharmS | Member, Royal Pharmaceutical Society |
| MRSC | Member, Royal Society of Chemistry |
| MRSL | Member, Order of the Republic of Sierra Leone |
| MRST | Member, Royal Society of Teachers |
| MRTPI | Member, Royal Town Planning Institute |
| MS | Master of Surgery; Master of Science (US); Mississippi |
| MSA | Master of Science, Agriculture (US); Mineralogical Society of America |
| MSAE | Member, Society of Automotive Engineers (US) |
| MSC | Manpower Services Commission; Missionaries of the Sacred Heart; Madras Staff Corps |
| MSE | Master of Science in Engineering (US) |
| MSF | (Union for) Manufacturing, Science, Finance |
| MSI | Member, Securities Institute |
| MSM | Meritorious Service Medal; Madras Sappers and Miners |
| MSocIS | Member, Societe des Ingenieurs et Scientifiques de France |
| MSR | Member, Society of Radiographers |
| MSW | Master, Social Work/Welfare |
| MT | Mechanical Transport; Montana |
| MTAI | Member, Institute of Travel Agents |
| MTB | Motor Torpedo Boat |
| MTD | Midwife Teachers' Diploma |
| MTech | Master of Technology |
| MTh | Master of Theology |
| MusB | Bachelor of Music |
| MusD | Doctor of Music |
| MusM | Master of Music |
| MVO | Member, Royal Victorian Order |