Schickele describes P. D. Q. Bach as having "the originality of Johann Christian, the arrogance of Carl Philipp Emanuel, and the obscurity of Johann Christoph Friedrich." The most distinguishing feature of P. D. Q. Bach's music, in the words of Schickele, is "manic plagiarism".
P. D. Q. Bach seldom wrote original tunes; he stole melodies from other composers and rearranged them in often funny ways. P. D. Q. Bach's music uses instruments not often used in orchestras, such as the tromboon, slide whistle, hardart, lasso d'amore, left-handed sewer flute and kazoo, as well as items not normally used as musical instruments, such as balloons, fog horns, and bicycles. His music also calls for unusual methods of playing traditional instruments, such as blowing through double reeds by themselves (that is, detached from the instruments) throughout Iphigenia in Brooklyn. His parts for vocalists include coughing, snoring, sobbing, laughing and yelling.
P. D. Q. Bach's work pokes fun at music including Baroque, Romantic, modern, country music (Oedipus Tex and Blaues Gras), and rap (Classical Rap). The "Schickele" or "S." numbers whimsically assigned to P. D. Q. Bach's works parody musicologists' catalogues of famous composers, such as the Köchel catalogue of Mozart's works.
There is often a startling juxtaposition of styles within a single P. D. Q. Bach piece. The Prelude to Einstein on the Fritz, which alludes to Philip Glass's opera Einstein on the Beach, provides an example. The underlying music is J.S. Bach's first prelude from The Well-Tempered Clavier, but with each phrase repeated interminably in a minimalist manner that parodies Glass's. On top of this mind-numbing structure is added everything from jazz phrases to snoring to the chanting of a meaningless phrase ("Koy Hotsy-Totsy," alluding to the art film Koyaanisqatsi for which Glass wrote the score). Through all these mutilations, the piece never deviates from Bach's original harmonic structure.
The humor in P. D. Q. Bach music often derives from violation of audience expectations, such as repeating a tune more than the usual number of times, resolving later than usual or not at all, unusual key changes, or sudden switches from high art to low art.
Schickele divides P. D. Q. Bach's musical output into three periods: the Initial Plunge, the Soused Period, and Contrition.
During the Initial Plunge, P. D. Q. Bach wrote the Traumerai for solo piano, an Echo Sonata for "two unfriendly groups of instruments", and a Gross Concerto for Divers Flutes, two Trumpets, and Strings.
During the Soused (or Brown-Bag) Period, P. D. Q. Bach wrote a Concerto for Horn & Hardart, a Sinfonia Concertante, a Pervertimento for Bicycle, Bagpipes, and Balloons, a Serenude, a Perückenstück (literally German for "Hair-piece"), a Suite from The Civilian Barber (spoofing Rossini's The Barber of Seville), a Schleptet in E-flat major, the half-act opera The Stoned Guest (the character of "The Stone Guest" from Mozart's Don Giovanni), a Concerto for Piano vs. Orchestra, Erotica Variations (Beethoven's Eroica Variations), Hansel and Gretel and Ted and Alice, an opera in one unnatural act (Humperdinck's Hansel and Gretel and the 1969 film Bob & Carol & Ted & Alice), The Art of the Ground Round (Bach's The Art of Fugue), a Concerto for Bassoon vs. Orchestra, and a Grand Serenade for an Awful Lot of Winds and Percussion.
During the Contrition Period, P. D. Q. Bach wrote the cantata Iphigenia in Brooklyn (Gluck's Iphigenia in Aulis, etc.), the oratorio The Seasonings (Haydn's The Seasons), Diverse Ayres on Sundrie Notions, a Sonata for Viola for Four Hands, the chorale prelude Should, a Notebook for Betty Sue Bach (Bach's Notebook for Anna Magdalena Bach and Buddy Holly's "Peggy Sue"), the Toot Suite, the Grossest Fugue (Beethoven's Grosse Fuge), a Fanfare for the Common Cold (Copland's Fanfare for the Common Man), and the canine cantata Wachet Arf! (Bach's Wachet auf).