MaxQ
- 2007 Barbershop Harmony Society International Champion Quartet
- http://www.maxquartet.com

McKenzie Touring Co
- Comedy quartet from Eugene, Oregon who have performed in ten different states: Alaska, Washington, California, Oregon, Idaho, Montana, Colorado, Nebraska, Kansas,and Weird.
- http://www.cascadechorus.org/McKenzie.asp

Mirage
- A classy quartet from North Bay, Ontario, Canada. 
- http://www.miragequartet.com/

Moonglow
- A male a capella quartet singing close harmonies, mainly in the Barbershop style. Based in Edinburgh but travel throughout Scotland.
- http://moonglow.org.uk

Most Happy Fellows
- 1977 International Quartet Champions from Seattle Washington.
- http://www.mosthappyfellows.com/

Michigan Jake
- 2001 International Quartet Champions named after a Warner Brothers cartoon frog.
- http://www.michiganjake.com/

Marquis
- 1995 International Quartet Champions from Cincinnati, Ohio.
- http://www.harmonize.com/Marquis/Default.htm

Midnite Watchmen
- A mail carrier, a treasurer, an auctioneer and a musical director make up this foursome from Wisconsin and Minnesota.
- http://www.arneberg.com/bbshop/watchmen/

Metropolis
- An entertaining, humorous and musical SPEBBSQSA quartet, ranked among the top ten quartets in the world and featured on television and film. 1998 national a cappella champions.
- http://www.harmonize.com/metropolis/

The Musical Firm of Schwarzkopf, Anderson, Carney & Bray
- Comedy quartet from Shawnee Mission Kansas that boasts the longest name ever registered with SPEBSQSA.
- http://www.themusicalfirm.org

Management
- Originally met through the University of Maine system.they were all professional music educators and taught music at Middle and High Schools throughout New England.
- http://www.westbath.u47.k12.me.us/mgmt.htm

Missing 55
- The 1998 Illinois District High School Champion quartet from Chatham, Illinois
- http://www.harmonize.com/Missing55/