The long century of Debussy research since 1918 has featured competing insights into his ‘arabesque’ idea (Zenck 1974, Eigeldinger 1988, Bhogal 2013). Was this a melodic, polyphonic, or polysemic concept? Supporting Bhogal’s view of arabesque as diachronic and variable, we explain its three-decade-long evolution in Debussy’s music via early, intermediate, conventional and late stages. Our study applies music-analytical rigour to compositional evidence from across his output, representing a significant and original contribution to interpreting his development. Beyond explicating technical differences between his early and mature techniques, we show how arabesque taxonomy must extend past the L’Après-midi period into Debussy’s final decade, when he developed a ‘late’, transformed version of this practice. Finally, we argue that arabesque represents one of Debussy’s central stylistic discoveries, enabling him to link material to process, to conceive of melody, heterophony, and polyphony suited to the new formal principles that would inspire generations of future composers.