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- Yo-Yo Ma
- Robert MacNeil
- Howie Mandel, demonstrating "ticklish"
- Eric Mangini, one segment: Mangini, the New York Jets coach, appears during in season 38 (2007), along with other Jets, Elmo, and Elmo's goldfish Dorothy.
- Cheech Marin
- Julianna Margulies as Dr. Berger who helps heal Big Bird's broken wing
- Ziggy Marley
- Bruno Mars singing "Don't Give Up"
- Andrea Martin
- Steve Martin
- Marlee Matlin sings with Billy Joel
- John Mayer, in a Primetime Special that appears on April 1, 2009
- Whitman Mayo
- Martina McBride
- Jenny McCarthy, imitating several sorts of insect
- Bobby McFerrin
- Phil McGraw co-hosting with Dr. Feel
- Tim McGraw singing about sharing with his wife, Faith Hill
- Michael McKean Rock, Rock Band (episode 4234, season 41)
- Christopher Meloni
- Menudo
- Debra Messing
- Lin-Manuel Miranda as Freddy Flapman in episode 4187
- Julianne Moore
- Rick Moranis
- Rita Moreno
- Mark Morris
- Michael Moschen
- John Moschitta, Jr.
- Zero Mostel
- Jason Mraz
- Megan Mullally
Read more about this topic: List Of Guest Stars On Sesame Street