Karen-Marie Flagstad (November 24, 1904 – December 25, 1992) was a Norwegian soprano opera singer.
Flagstad was born in Oslo and was one of Norway's leading singers in her time. She was the sister of the world-renowned singer Kirsten Flagstad, and the daughter of the conductor Michael Flagstad and the pianist Maja Flagstad.
She played minor roles as part of her family's engagement with the short-lived Opera Comique (1918–1921), and had her serious stage debut (1926) as Hannah in Eduard Künneke's The Cousin from Nowhere. Another of her early roles was in Emmerich Kálmán's Die Bajadere. Her first major roles were as Amor in Christoph Willibald Gluck's Orfeo ed Euridice (Central Theater, 1933) and Giuiletta in Jacques Offenbach's The Tales of Hoffmann (National Theatre, 1938) under the direction of Olav Kielland.
Flagstad traveled abroad and sang on American radio. On the German stage, she played Salome in Richard Strauss's opera of the same name, and Ariadne in his Ariadne auf Naxos. She was married to the Austrian pianist Johann Crkal (1891–1939) and she performed in Italy and France as Karen Maria Crkal, first as a guest together with her sister as Brünnhilde at La Scala as Ortlinde in Wagner's Die Walküre (1949). She repeated the role in Rome (1952) and then in Bordeaux together with Beate Asserson (1954). She performed again at La Scala in 1953 as Wellgunde in Götterdämmerung.