The Casal Quartett (in English Casal Quartet, and often stylized casalQuartett or cQ) is one of the few major chamber groups to have built a substantial reputation performing on both modern and historical instruments. The quartet's large and varied repertory extends from the 17th century into contemporary music of various kinds.

The Casal Quartett was formed in 1996 in Zurich, Switzerland. It should not be confused with Spain's Casals Quartet. The group consists of violinists Felix Froschhammer and Rachel Späth, violist Markus Fleck, and cellist Andreas Fleck. The original group members were students of the Carmina Quartet in Basel, Switzerland, and the Alban Berg Quartet in Cologne, Germany. They went on for further lessons with Walter Levin in Basel and also benefited from master classes and other training with a variety of chamber music players and singers, including Martha Argerich, Fazil Say, and Emma Kirkby. The group has toured widely in Switzerland and Germany with a repertory that extends from the 17th century to the present day, with a large variety of music from tango to Karlheinz Stockhausen to music for children. A major new development in the quartet's career came in 2008 when it adopted the use of 17th century instruments made by the famous builder Jacob Steiner. Using these instruments, the Casal Quartett has specialized in works showing the development of the string quartet in the 18th century. For the 250th anniversary of Beethoven's birth in 2020, the quartet devised a "Beethoven's World" program that focused on the composer in relation to his contemporaries.

The Casal Quartet made its debut on recordings in 1999 with an album including quartets by Schubert and Janácek. The group has recorded mostly for the Solo Musica label; it has also worked with Telos, Bayer, and Guild, where it issued an album of 20th century Swiss quartets in 2006. The quartet's recorded repertory has been varied, extending from the quartets of 18th century composer Franz Xaver Richter to tango. In 2020, the group joined Fazil Say for the album Ballads Quintets, featuring works by Say and Schumann. ~ James Manheim, Rovi