This chapter can give only a flavour of the myriad ways in which twentieth-century composers extended the frontiers of string playing in their quartets and, hence, the timbral palette of ensembles. Restrictions of space allow only a general overview, together with some detailed discussions of specific trends, techniques and expressive effects, with pertinent examples from the repertory. In many respects the weight of Classical tradition and the perceived limitations in the technical possibilities of stringed instruments initially resulted in the genre resisting radical change to a greater extent than most other media. Despite the extraordinary variety and concentration of texture and timbres in Webern's Bagatelles Op. 9, for example, performers are consistently required to pursue their traditional roles of hearing and feeling as a unified ensemble, interpreting each note as belonging to a single melody of timbres.

This is in sharp contrast to the more individualistic roles encouraged later in the century, when the genre became a vehicle for remarkable experiment and radical compositional thought. Bartók's quartets, with their wide range of pizzicato effects, vibrato indications, col legno and microtones, provided the most significant spark to those composers seeking to expand the vocabulary of available sounds and timbres. The chromaticism, the rhythmic and metrical devices and the colouristic and textural use of glissandi in Bartók's Third Quartet, for example, were all highly unusual for the sometimes retrogressive 1920s; furthermore, Hindemith's contemporary Second Quartet (Op. 16) requires the second violinist to reiterate a figure without regard to the pulse of the other parts (finale, bb. 458–511), a technique tentatively foreshadowing the development of aleatory devices such as appeared in, for example, Gunter Schuller's First Quartet (1957), with its opportunities for improvisation.