This paper explores Nadia Boulanger's concept of la grande ligne (the "long line") and how its aesthetic principles of coherence and structure manifest in the French modernist works of Nadia and her sister, Lili. I expand and refine Jeanice Brook's work by proposing that la grande ligne may signify 1) an actual melodic line that holds a phrase or section together or 2) a tonal plan that strives for a coherent trajectory from its hierarchical elements. I begin with the works of Fauré as exemplar of la grande ligne and then track similar compositional procedures in the works of Nadia and Lili Boulanger, through the works of Debussy. Overall, I illustrate how compositions of the time enacted Boulanger’s construal of la grande ligne, arguing that an interpretation of it as literal contrapuntal line or abstract tonal plan is a useful point of departure for understanding and hearing numerous French compositions.