Heinz-Klaus Metzger (6 February 1932 – 25 October 2009) was a German music critic and theorist. Born in Konstanz, Metzger studied piano under Carl Seemann in Freiburg im Breisgau and composition under Max Deutsch in Paris. Later, he met Theodor W. Adorno, Edgard Varèse, Karlheinz Stockhausen and Luigi Nono at the Darmstadt International Summer Courses for New Music. Here he found his role as a notable theoretician and proponent of serialism in musical theory. He participated as a distinguished contributor to a series of important texts in the journal Die Reihe. Metzger was among the first critics to promote Stockhausen's music, but was soon a substantial critic of Stockhausen's compositional development.