- Mass General Brigham
- Massachusetts Attorney General
- Massachusetts Coalition for Serious Illness Care
- Massachusetts General Hospital
- Massachusetts Hospital Association
- Massage Envy
- Massasoit Community College
- MassHealth
- Match.com
- Mathematica Policy Research
- Mather LifeWays Institute on Aging
- MatrixCare
- Matter Health
- Mavencare
- Maxim
- Maxim Healthcare Services
- Maxim Healthcare Staffing
- Maxwell Group
- Maxwell Healthcare Associates
- Maya Home Health Care Corp