Michael Andreas Gielen (20 July 1927 – 8 March 2019) was an Austrian conductor and composer known for promoting contemporary music in opera and concert. Principally active in Europe, his performances are characterized by precision and vivacity, aiding his ability to interpret the complex contemporary music he specialized in.

He first worked in Buenos Aires, where he lived with his family between 1938 and 1950. In Europe, he first worked in Vienna and then in Sweden as the Generalmusikdirektor (GMD) of the Royal Swedish Opera. He conducted notable world premieres such as György Ligeti's Requièm, Karlheinz Stockhausen's Carré, and Bernd Alois Zimmermann's opera Die Soldaten and his Requiem für einen jungen Dichter. He directed the Oper Frankfurt from 1977 to 1987, installing more contemporary operas, winning stage directors such as Hans Neuenfels and Ruth Berghaus, and reviving operas such as Schreker's Die Gezeichneten. During his era, the company became one of the leading operas.

Gielen was also principal conductor of the National Orchestra of Belgium (1969–1973), the Cincinnati Symphony Orchestra (1980–1986) and the Southwest German Radio Symphony Orchestra (1986–1999). As a composer, he worked in the tradition of the Second Viennese School, often setting modern literature to music. His works were premiered with performers such as Joan Carroll, Siegfried Palm, Aloys Kontarsky and the LaSalle Quartet.