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- Maggini Quartet
- Mandelring Quartet
- Mandeville Quartet
- Manor House Music String Quartet
- Marian Anderson String Quartet
- Marie Hall Quartet led by Marie Hall
- Martinů Quartet
- Mazerska Kvartett 'Uskapet'
- Meccorre String Quartet
- Mecklenburg Quartet (Saint Petersburg), Квартет герцога Мекленбургского (Russian Wikipedia)
- Medici Quartet
- Melbourne Youth Quartet
- Melos Quartet
- Mendelssohn Quartet
- The Merchant Quartet
- Miami String Quartet
- Miró Quartet
- Moyzes Quartet
Read more about this topic: List Of String Quartet Ensembles