This article provides new perspectives on Claude Debussy's compositional process in his String Quartet through a fresh examination of existing sources, particularly a sketchbook kept in the Bibliothèque nationale de France. First, the fragmentary nature of the material contained in the sketchbook implies the existence of another manuscript, now lost. By analyzing Debussy's notations for his String Quartet in greater detail, it is possible to question the different functions the latter took on in the compositional process: in addition to the musical ideas simply noted as an aide-memoire, there are more exploratory musical fragments. Furthermore, the description and analysis of the sources of the String Quartet's creative process enhance our knowledge of Debussy's compositional methods and techniques. These new insights into the sources also show how Debussy adapted to certain social and aesthetic constraints when writing the String Quartet. The compositional context, the very genre of the quartet, and the fact that Debussy was close to Chausson and the Société nationale, led him to seek compositional solutions to combine the techniques of the Franck school with the personal aesthetic he was developing at the time. In particular, the article reconstructs part of the composer's reflection on the cyclic design, which is at the heart of the questions raised in the sketches.