Ionisation (1929–1931) is a musical composition by Edgard Varèse written for thirteen percussionists. It was among the first concert hall compositions for percussion ensemble alone, although Alexander Tcherepnin had composed an entire movement for percussion alone in his Symphony No. 1 from 1927. In the journal Tempo, percussionist Brian Holder writes, "The work presented the important notion that unpitched percussion (with piano and other pitched instruments coming in at the end) could stand alone as a serious form of concert music – a relatively unexplored concept at the time."

The premiere was at Carnegie Chapter Hall, an annex to New York City's Carnegie Hall, on March 6, 1933, conducted by Nicolas Slonimsky, to whom the piece was later dedicated. One critic described the performance as "a sock in the jaw".