| Abbreviation | Definition |
|---|---|
| MIS | Master Investigative Staff |
| MISUR | MIcrophone SURveillance |
| MIT | Murder Investigation Team |
| MM | Miami Field Office |
| MO | Mobile Field Office |
| MO | Modus Operandi |
| MOI | Manual Of Instructions |
| MOS | Man On the Street |
| MOSJ | Environmental Monitoring of Svalbard and Jan Mayen |
| MOSNAT | MOvement of Soviet NATionals |
| MP | Minneapolis Field Office |
| MRB | Management Review Board |
| MS | MiSsing |
| MSC | MiSCellaneous |
| MST | Mobile Strike Team |
| MSTN | Mid-South Tactical Network |
| NA | National Academy |
| NA | Not Applicable |
| NAC | New Agents Class |
| NARA | National Archives and Records Administration |