The string quartets of Bartók, each written in a considerably different style, as a six-piece series became from the 1950s on an almost unrivaled standard of the 20th-century repertoire in this esteemed genre. One constituent of the quickly rising attractiveness and worldwide high-quality interpretation was that Bartók's notation for string quartet appeared to be much more precise, elaborated, and consistent than e.g. the notation of different work groups in his piano music. His idiomatic and innovative writing for strings in a way exercised greater impact on post-war composers than Bartók's compositional system. Based on recent source studies connected with the editorial work on the forthcoming two string quartet volumes of the Bartók critical edition I will discuss: (1) preliminary and revised concepts of the whole work or individual movements in string quartets nos. 1 and 3-6 on the evidence of sketches and the draft; (2) the significance of past and contemporary models and influences; (3) text corruption in no.1, notational problems in no. 2; (4) the source value of the four known contemporary recordings (1925 no. 2 by Amar-Hindemith, 1936 no. 1 by Pro Arte, 1936 no. 2 by Budapest, 1941 no. 5 by Kolisch Quartet).