This chapter demarcates two eras of piano composition – pre-Debussy and post-Debussy – by taking as its focal point a comment made by the pianist Marguerite Long that since Debussy no one has heard or played the piano in the same way as it was played before. As crude as these delineations are, the goal is to emphasise the truly transformative nature of his approach to thinking about the piano in its entirety – as a technological machine, a source of unlimited and variegated sonority, and a catalyst for freeing the human imagination. While taking into consideration the pianistic tradition that Debussy was born into and the one that he was propelled towards – spurred on by the innovations of his contemporaries at the piano, including Gabriel Fauré, Emmanuel Chabrier, and Maurice Ravel – this chapter highlights Debussy’s uniquely refined sense of how the piano might be made to sound anew. By the turn of the twentieth century he was beginning to establish his status as a trailblazer at the keyboard. It would be up to his immediate successors, particularly the French composers Olivier Messiaen and Pierre Boulez, to extend the expressive potential of his engagement with the sensual, dramatic, and formal potentials of sound into a dimension that exploited aspects of acoustics and resonance.