Klaus Tennstedt (June 6, 1926 – January 11, 1998) was a German conductor from Merseburg. He studied violin and piano at the Leipzig Conservatory. He became concertmaster of the orchestra at the Halle Municipal Theatre in 1948. However, a finger injury stopped his career as a violinist, and afterwards he worked as a coach to singers at the same theatre. Tennstedt then directed his talents toward conducting. In 1958, he became music director of the Dresden Opera, and in 1962, music director of the Schwerin State Orchestra and Theatre.

Tennstedt emigrated from East Germany in 1971 and obtained asylum in Sweden. He conducted in Gothenburg with the Göteborg Theatre and in Stockholm with the Swedish Radio Symphony Orchestra. In 1972, he became General Music Director of the Kiel Opera in Northern Germany. From 1979 to 1982, he served as Chief Conductor of the North German Radio Orchestra in Hamburg.

In 1974, Tennstedt made his North American debut with the Toronto Symphony Orchestra. His first US appearance was shortly after that, with the Boston Symphony Orchestra, in December 1974, conducting Bruckner's Symphony No. 8. In Norman Lebrecht's The Maestro Myth, the story was told that when the Boston management asked Tennstedt what he wanted to conduct, he replied: "You mean I get to choose?" His appearances were highly acclaimed, and as a result, Tennstedt guest-conducted at the Tanglewood Music Festival in 1975. His USA opera debut was at the Metropolitan Opera, New York, in 1983, conducting a production of Beethoven's Fidelio. He also guest-conducted with the Philadelphia Orchestra, the Chicago Symphony Orchestra, and the New York Philharmonic Orchestra.

His London debut was with the London Symphony Orchestra in 1976. In 1977 came his first engagement with the London Philharmonic Orchestra (LPO), which led to his appointment as the LPO's Principal Guest Conductor in 1980, and eventually as Principal Conductor in 1983. Due to ill-health, however, he stepped down in 1987, and he was later named the LPO's Conductor Laureate. He did return to the LPO for concerts of Mahler in November 1991 (Symphony No. 6) and May 1993 (Symphony No.7). However, on the advice of his physicians, Tennstedt retired from conducting altogether in October 1994.

His recordings include a complete cycle of the symphonies of Gustav Mahler. Several of Tennstedt's concert performances have been reissued on CD.