Michael Gielen (born July 20, 1927) is an Austrian conductor and composer.
He began his career as a pianist in Buenos Aires, having studied there with Erwin Leuchter, giving an early performance of Schoenberg's complete piano works. While serving as conductor and repetiteur at the Wiener Staatsoper (1951-1960), Gielen conducted much contemporary music outside the opera house. His next operatic appointment was as conductor of the Royal Opera in Stockholm (1960-1965), followed by posts at the Netherlands Opera and the Frankfurt Opera. He was principal conductor of the Belgian National Orchestra (1969-) and of the Cincinnati Symphony (1980-1986).