The longest and at the same time most complex of Bartók’s six string quartets was composed in the summer of 1934 as a well-paid commission for the renowned Elisabeth Sprague Coolidge Foundation in Washington. Bartók wrote it in a few weeks in Budapest. The substantially reworked autograph shows us how hard he laboured on the elaborate five-movement form. In the run-up to the premiere, he clarified numerous questions concerning the execution – including specific practice instructions for the “Bulgarian rhythm” of the third movement – with the first violinist of the Kolisch Quartet. László Somfai and Zsombor Németh present this and other essential information for the performance practice of the quartet in their Urtext edition, which is based on an extensive group of sources. It also includes Bartók’s own analysis of the work. Together with clearly engraved notation and convenient page turns in the parts, it provides an optimal basis for playing this masterpiece of modern quartet literature.