| MCLS | Madison County Library System 
| Others |
| MCLS | Management Consulting Listbroking Services
| Others |
| MCLS | Manitowoc Calumet Library System
| Others |
| MCLS | Manufactured Cannabis Licensing System
| Others |
| MCLS | Mathematical Cognition and Learning Society
| Others |
| MCLS | Members Council on Library Services
| Others |
| MCLS | Metropolitan Cooperative Library System
| Others |
| MCLS | Midwest Collaborative for Library Services
| Others |
| MCLS | Modern and Classical Language Studies
| Others |
| MCLS | Molecular and Cellular Life Sciences
| Others |
| MCLS | Monroe County Library System
| Others |
| MCLS | Muskingum County Library System
| Others |