Agathe Ursula Backer Grøndahl (1 December 1847 – 4 June 1907) was a Norwegian pianist and composer. She married the conductor and singing teacher Olaus Andreas Grøndahl in 1875, and was generally known thereafter as Agathe Backer Grøndahl. Her son Fridtjof Backer-Grøndahl (1885-1959) was also a pianist and composer, who promoted his mother's compositions in his concerts.
Agathe Backer was born in Holmestrand in 1847, in a wealthy and art-loving home, as the second youngest of four sisters, all gifted in drawing and music. In 1857 she moved with her family to Christiania, where she studied with Otto Winther-Hjelm, Halfdan Kjerulf and Ludvig Mathias Lindeman. Between 1865-1867 she became a pupil of Theodor Kullak and studied composition under Richard Wuerst at the Akademie der Tonkunst in Berlin, where she lived together with her sister Harriet Backer. She won fame there with her interpretation of Beethoven's "Emperor" Concerto.
In 1868 she debuted with Edvard Grieg, then 26 years old, as conductor of the Philharmonic Society. A recommendation from Ole Bull led to further studies with Hans von Bülow in Florence in 1871. Later the same year she played at the Gewandhaus in Leipzig, becoming a pupil of Franz Liszt in Weimar in 1873. In 1875 she was married to the celebrated singing teacher Herr Grondahl of Christiania, and during the second half of the 1870s she built up an outstanding pianist career with a series of concerts in the Nordic countries, also playing with very great success in London and Paris.