La Mer stands at the center of Debussy’s achievement. Described by the composer as a seascape without figures, it is arguably the greatest and most original French symphony. In this study, La Mer is considered in the context of Debussy’s personal and musical development. Detailed discussion of performance styles draw on current recordings, and two analytical chapters trace the growth of ideas through the work. Studies of rhythm, motif and tonality show how Debussy generates narratives across the three movements.