Saint-Saëns' early start and his long life provided him with time to write hundreds of compositions; during his career, he wrote many dramatic works, including four symphonic poems, and thirteen operas, of which Samson et Dalila and the symphonic poem Danse Macabre are among his most famous. In all, he composed over 300 works and was the first major composer to write music specifically for the cinema, for Henri Lavedan's film The Assassination of the Duke of Guise (Op. 128, 1908).
Saint-Saëns wrote five symphonies, although only three of these are numbered. He withdrew the first, written for a Mozartian-scale orchestra, and the third, a competition piece. His symphonies are a significant contribution to the genre during a period when the French symphonic tradition was otherwise in decline. Saint-Saëns also contributed voluminously to the French concertante literature; he wrote five piano concertos, three violin concertos, two cello concertos, and about twenty smaller concertante works for soloist and orchestra, including a colorfully orchestrated piano fantasy, Africa; the Havanaise and the Introduction and Rondo capriccioso for violin and orchestra; and the Morceau de Concert for harp and orchestra. Of the concertos, the Second, Fourth and Fifth Piano concertos, the Third Violin Concerto, and the First Cello Concerto remain popular. Indeed, Saint-Saëns's Concerto in G minor is one of the most popular virtuoso piano concertos of all time, but when Saint-Saëns heard Harold Bauer play it, he said, "That is very good, but please remember that I wrote five piano concertos: FIVE."
In 1886 he wrote his final symphony, the Symphony No. 3, avec orgue (with organ), one of his best-known works. Aided by the monumental symphonic organs built in France by Aristide Cavaillé-Coll, at that time the world's foremost organ builder, this work demonstrates the spirit of "gigantism" and the confidence of France at the end of the 19th century, a period that also produced the Eiffel Tower, the Universal Exposition at Paris and the Belle Époque. The confident Maestoso fourth movement perhaps reflects the confidence of Europe in its technology, its science, its "age of reason". He was frequently named as "the most German of all the French composers", perhaps due to his use of counterpoint.
In 1886, Saint-Saëns completed Le Carnaval des Animaux, which was first performed on 9 March. Despite the work's great popularity today, Saint-Saëns forbade complete performances of it shortly after its première, allowing only one movement, Le Cygne (The Swan), a piece for cello and two pianos, to be published in his lifetime. Carnival was written as a musical jest, and Saint-Saëns believed it would damage his reputation as a serious composer. In fact, since its posthumous publication, this work's imagination and musical brilliance have impressed both ordinary listeners and music critics.