The Tosca String Quartet is Leigh Mahoney (violin), Tracy Seeger (violin), Ames Asbell (viola), and Sara Nelson (cello). They began in 1996 as members of the Tosca Tango Orchestra, a seven-piece ensemble from Austin, Texas. The tango nuevo orchestra performed new compositions by bandleader Glover Gill (along with a few Astor Piazzolla covers) and released six albums. In 2000, the group gained an international following with soundtrack and on-screen work in Richard Linklater's film Waking Life, and an appearance at the 5th World Tango Summit in Argentina. The quartet continues to perform with Gill and his group, Glovertango, whenever possible.

In 1999, the Tosca String Quartet began presenting concerts of new music by local composers in alternative performance spaces, often bars and clubs. These collaborations led to the Golden Hornet Project (founded by Graham Reynolds and Peter Stopschinski) and ongoing relationships with several local composers, including Terry Bozzio of Frank Zappa and Missing Persons fame.

The members of the quartet form the core of The Tosca Strings, who toured internationally with David Byrne from 2001 to 2005 and were featured on his Grown Backwards album. The quartet also appears on the Dixie Chicks' album Home, and has recorded and/or performed with artists such as Spoon, Bonnie Raitt, Ray LaMontagne, Susana Baca, Bob Schneider, Ian McLagan, Ray Benson, Vampire Weekend and DeVotchKa. Tosca also performs in the Austin-based project Erik and the She-Wolves, with fiddler/guitarist Erik Hokkanen in a show that includes bluegrass, fiddle, surf, western and gypsy swing styles.

Alongside their pop music activities, the quartet remains a part of Austin's classical scene. The group frequently performs concerts of contemporary chamber music throughout the area. They recorded a series of movie scores in 2007, working with Andres Levin and Stephen Barber for El Cantante, Borderland, and Ladron Que Roba a Ladron. The quartet are also founding members of the American Repertory Ensemble, a contemporary chamber music & dance collective.