Cage was an early composer of what he called "chance music" (and what others have decided to label aleatoric music)—music where some elements are left to be decided by chance; he is also well known for his non-standard use of musical instruments and his pioneering exploration of electronic music. His works were sometimes controversial, but he is generally regarded as one of the most important composers of his era, especially in his raising questions about the definition of music.

John Cage put Zen Buddhist beliefs into practice through music. He described his music as "purposeless play", but "this play is an affirmation of life—not an attempt to bring order out of chaos, nor to suggest improvements in creation, but simply to wake up to the very life we are living, which is so excellent once one gets one's mind and desires out the way and lets it act of its own accord."

Cage was also an avid amateur mycologist and mushroom collector: he co-founded the New York Mycological Society with three friends. He was a long-term collaborator and romantic partner of choreographer Merce Cunningham.