César Auguste Jean Guillaume Hubert Franck (French: [sezaʁ oɡyst ʒɑ̃ ɡijom ybɛʁ fʁɑ̃k]; 10 December 1822 – 8 November 1890) was a French Romantic composer, pianist, organist, and music teacher born in present-day Belgium.

He was born in Liège (which at the time of his birth was part of the United Kingdom of the Netherlands). He gave his first concerts there in 1834 and studied privately in Paris from 1835, where his teachers included Anton Reicha. After a brief return to Belgium, and a disastrous reception of an early oratorio Ruth, he moved to Paris, where he married and embarked on a career as teacher and organist. He gained a reputation as a formidable musical improviser, and travelled widely within France to demonstrate new instruments built by Aristide Cavaillé-Coll.

In 1859, he became titular organist at the church Sainte-Clotilde, a position he retained for the rest of his life. He became professor at the Paris Conservatoire in 1872; he took French nationality, a requirement of the appointment. After acquiring the professorship, Franck wrote several pieces that have entered the standard classical repertoire, including symphonic, chamber, and keyboard works for pipe organ and piano. As a teacher and composer he had a vast following of composers and other musicians. His pupils included Ernest Chausson, Vincent d'Indy, Henri Duparc, Guillaume Lekeu, Albert Renaud, Charles Tournemire and Louis Vierne.

His best known works include Symphony in D minor, the Violin Sonata and a setting of the Panis angelicus.

Franck was born in Liège, then part of the United Kingdom of the Netherlands, to Nicolas-Joseph Franck (1794–1871), a bank clerk whose family came from the then German-Dutch border, and Marie-Catherine-Barbe Franck (née Frings, 1788–1860), who was from Aachen, Germany. Although young César-Auguste, as he was known in his early years, showed both drawing and musical skills, his father envisioned him as a young prodigy pianist-composer, after the manner of Franz Liszt or Sigismond Thalberg, who would bring fame and fortune to his family. His father entered Franck at the Royal Conservatory of Liège, studying solfège, piano, organ, and harmony with Joseph Daussoigne-Méhul and other faculty members. César-Auguste gave his first concerts in 1834, one before Leopold I of the newly formed Kingdom of Belgium.

In 1835, his father resolved that the time had come for wider audiences, and brought César-Auguste and his younger brother Joseph to Paris, to study privately: harmony and counterpoint with Anton Reicha, piano with Pierre Zimmerman, and solfège with Hippolyte-Raymond Colet. When Reicha died some ten months later, Nicolas-Joseph sought to enter both boys into the Paris Conservatoire. However, the Conservatoire would not accept foreigners; Nicolas-Joseph was obliged to seek French citizenship, which was granted in 1837. In the interval, Nicolas-Joseph promoted concerts and recitals in Paris featuring one or both boys playing popular music of the period, to mostly good reviews.

Young Franck and his brother entered the Conservatoire in October 1837, César-Auguste continuing his piano studies under Zimmerman and beginning composition with Aimé Leborn. He took the first prize in piano at the end of his first year (1838) and consistently maintained that level of performance. His work in counterpoint was less spectacular, taking successively third, second, and first prizes between 1838 and 1840. He added organ studies with François Benoist, which included both performance and improvisation, taking second prize in 1841, with the aim of competing for the Prix de Rome in composition in the following year. However, for reasons that are not explicit, he made a "voluntary" retirement from the Conservatoire on 22 April 1842.

His withdrawal may have been at his father's behest. While César-Auguste was pursuing his academic studies, he was, at his father's demand, also teaching privately and giving concerts. "It was a hard life for him, . . . and not made easier by the ill-tempered and even vindictive behavior of his father . . . ." Concerts performed by young Franck (some with his brother on the violin, some including Franck's own compositions) were at first received well, but increasingly Nicolas-Joseph's commercial promotion of his sons antagonized the Parisian musical journals and critics. César-Auguste's technical abilities as a pianist were acknowledged; his abilities as a composer were (probably justly at this point) felt to be wanting. The whole situation was aggravated by what in the end became a feud between Nicolas-Joseph and Henri Blanchard, the principal critic of the Revue et Gazette musicale, who lost no opportunity to castigate the aggressive pretensions of the father and to mock the "imperial" names of the elder son. This animosity, "undoubtedly personal", may well have caused Nicolas-Joseph to decide that a return to Belgium was in order, and in 1842 "a peremptory order" to young Franck compelled the latter to leave the Conservatoire and accompany him.