Marie-Alphonse-Nicolas-Joseph Jongen (14 December 1873 – 12 July 1953) was a Belgian organist, composer, and music educator.

Jongen was born in Liège. On the strength of an amazing precocity for music, he was admitted to the Liège Conservatoire at the extraordinarily young age of seven, and spent the next sixteen years there. Jongen won a First Prize for Fugue in 1895, an honors diploma in piano the next year, and another for organ in 1896. In 1897, he won the prestigious Prix de Rome, which allowed him to travel to Italy, Germany and France.

He began composing at the age of 13, and immediately exhibited exceptional talent in that field too. By the time he published his Opus 1, he already had dozens of works to his credit. His monumental and massive First String Quartet was composed in 1894 and was submitted for the annual competition for fine arts held by the Royal Academy of Belgium, where it was awarded the top prize by the jury.

In 1902, he returned to his native land, and in the following year he was named a professor of harmony and counterpoint at his old Liège college. With the outbreak of World War I, he and his family moved to England where he founded a piano quartet. When peace returned, he came back to Belgium and was named professor of fugue at the Royal Conservatoire in Brussels. From 1925 until 1929, he served as director of that institution; a quarter of a century after leaving the directorship, he died at Sart-lez-Spa, Belgium.

From his teens to his seventies Jongen composed a great deal, including symphonies, concertos (for cello, for piano and for harp), chamber music (notably a late string trio and three string quartets), and songs, some with piano, others with orchestra. (His list of opus numbers eventually reached 241, but he destroyed a good many pieces.) Today, the only part of his oeuvre performed with any regularity is his output for organ, much of it solo, some of it in combination with other instruments.

His monumental Symphonie Concertante of 1926 is a tour de force, considered by many to be among the greatest works ever written for organ and orchestra.[1] Numerous eminent organists of modern times (such as Virgil Fox, Jean Guillou, and Michael Murray) have championed and recorded it. The work was commissioned by Rodman Wanamaker for debut in the Grand Court of his palatial Philadelphia department store, Wanamaker's. Its intended use was for the re-dedication of the world's largest pipe organ there, the Wanamaker Organ. as part of a series of concerts Rodman Wanamaker funded with Leopold Stokowski and the Philadelphia Orchestra. Mr. Wanamaker's death in 1928 precluded the performance of the work at that time in the venue for which it was written, but it was finally performed for the first time with the Wanamaker Organ and the Philadelphia Orchestra on 27 September 2008.