For Schumann the four notes were encoded puzzles, and he predicted that "deciphering my masked ball will be a real game for you." The 21 pieces are connected by a recurring motif. In each section of Carnaval there appears either or both of two series of musical notes. These are musical cryptograms, as follows:
- A, E-flat, C, B - signified in German as A-S-C-H
- A-flat, C, B - signified in German as As-C-H
- E-flat, C, B, A - signified in German as S-C-H-A.
The first two spell the German name for the town of Asch (this is now Aš in the Czech Republic), in which Schumann's then fiancée, Ernestine von Fricken, was born. The sequence of letters also appears in the German word Fasching, meaning carnival. Asch is also German for "Ash," as in Ash Wednesday, the first day of Lent. It also encodes a version of the composer's name, Robert Alexander Schumann. The grouping S-C-H-A encodes the composer's name again with the musical letters appearing in Schumann, in their correct order.
Carnaval had its origin in a set of variations on a Sehnsuchtswalzer by Franz Schubert, whose music Schumann had only discovered in 1827. The catalyst for writing the variations may have been a work for piano and orchestra in the form of variations on the same Schubert theme, by Schumann's close friend Ludwig Schuncke. Schumann felt that Schuncke's heroic treatment was an inappropriate reflection of the tender nature of the Schubert piece, so he set out to approach his Variations in a more intimate way. He worked on his variations in 1833 and 1834. The work was never completed, however, and Schuncke died in December 1834, but Schumann did re-use the opening 24 measures for the opening of Carnaval. Andreas Boyde has since reconstructed the original set of Variations from Schumann's manuscript; Romanian pianist Herbert Schuch has recorded this reconstruction, with his own editorial amendations, for the Oehms Classics label.
In Carnaval, Schumann goes further musically than in Papillons, Op. 2, for in it he himself conceives the story of which it was the musical illustration. Each piece has a title, and the work as a whole is a musical representation of an elaborate and imaginative masked ball during carnival season. Carnaval remains famous for its resplendent chordal passages and its use of rhythmic displacement, and has long been a staple of the pianist's repertoire.
Schumann dedicated the work to the violinist Karol Lipiński.
Both Schumann and his wife, Clara, considered his solo piano works too difficult for the general public. (Frédéric Chopin is reported to have said that Carnaval was not music at all although Chopin did not warm to Schumann on the two occasions they met briefly, and had a generally low opinion of his music). Consequently, the works for solo piano were rarely performed in public during Schumann's lifetime, although Franz Liszt performed selections from Carnaval in Leipzig in 1840. However, today, despite its immense technical and emotional difficulty, it is one of Schumann's most often performed works.
Heinz Dill has mentioned Schumann's use of musical quotes and codes in this work. Eric Sams has discussed literary allusions in the work, such as to novels of Jean-Paul.