- Maryland Department of the Environment
- Maryland Hospital Association
- Maryland Office of Tourism
- Maryland Society of Association Executives
- Marymount Manhattan College
- Marywood University
- Mascaro Construction Co. L.P.
- MasiMax Resources, Inc.
- Masonic Care Community of New York
- Masonic Nursing Home Inc.
- Masonic Retirement Village
- Mass Mutual
- Massachusetts Assistance Centers
- Massachusetts College of Pharmacy and HS
- Massachusetts Convention Center Authority
- Massachusetts Department of Public Health
- Massachusetts Department of Public Health, EMSC
- Massachusetts General Hospital
- Massachusetts League of Community Health Centers, Inc.
- Massena Memorial Hospital
- Massey Escort Service
- MasterCare
- Matagorda County United Way
- Mathematics And Technology Help, Inc.
- Mather Hospital
- Matinair, Inc.
- Matlen Silver Enterprise Solutions
- Matrix Group International Inc.
- Matt Birk and Company
- Mattel
- Matthews Brothers Builders
- Matthews Photography, Inc.
- Maui The Magic Island
- Maui United Way
- Max Yield Cooperative
- Maxim Healthcare Services
- Maximus
- Maximus
- Maximus
- Mayaguez Medical Center
- Mayo Clinic
- Mayo Clinic - Jacksonville
- Mayo Clinic Florida
- Mayo Clinic Health System
- Mayo Clinic Health System in Eau Claire
- Mayo Clinic Health System in Eau Claire-Luther Campus
- Mayo Clinic Hospital
- Mayo Clinic Hospital, Methodist Campus
- Mayo Clinic Rochester Transplant Center
- Mayo Clinic-Saint Marys and Methodist Hospitals