Charles Ives's Symphony No. 4, S. 4 (K. 1A4) was written between 1910 and the mid-1920s (the second movement "Comedy" was the last to be composed, most likely in 1924). The symphony is notable for its multilayered complexity—typically requiring two conductors in performance—and for its large and varied orchestration. Combining elements and techniques of Ives's previous compositional work, this has been called "one of his most definitive works"; Ives' biographer, Jan Swafford, has called it "Ives's climactic masterpiece".