| Abbreviation | Definition |
|---|---|
| MRRC | Macomb Reference Research Center |
| MSDL | Montana State Digital Library |
| MSEL | Milton S Eisenhower Library |
| MSL | Maine State Library |
| MSL | Materials Systems Laboratory |
| MSL | Medical Sciences Library |
| MSL | Montana State Library |
| MSLA | Massachusetts School Library Association |
| MST | St. Cloud State University, St. Cloud, Minnesota, library code |
| MSTL | Minnesota Science Technology Library |
| MT | Masoretic Text |
| MT | Morphemic Translation |
| MTL | Monads Transformers Library |
| MTL | Multiplayer Traffic Library |
| MTLA | Mark Twain Library Association |
| MTLA | Minnesota Theological Library Association |
| MTPL | Manheim Township Public Library |
| MTPL | Middletown Township Public Library |
| MTTL | Multi Thread Template Library |
| MUA | Marquette University Archives |