Pachelbel's Canon (also known as Canon in D, P 37) is an accompanied canon by the German Baroque composer Johann Pachelbel (1653–1706). The canon was originally scored for three violins and basso continuo and paired with a gigue, known as Canon and Gigue for 3 violins and basso continuo. Both movements are in the key of D major. The piece is constructed as a true canon at the unison in three parts, with a fourth part as a ground bass throughout. Neither the date nor the circumstances of its composition are known (suggested dates range from 1680 to 1706), and the oldest surviving manuscript copy of the piece dates from 1838 to 1842.

Like his other works, Pachelbel's Canon went out of style, and remained in obscurity for centuries. A 1968 arrangement and recording of it by the Jean-François Paillard chamber orchestra gained popularity over the next decade, and in the 1970s the piece began to be recorded by many ensembles, while elements of the piece, especially its chord progression, were used in a variety of pop songs. By the early 1980s its presence as background music was deemed inescapable. The composition has since found increasingly common use in weddings and funeral ceremonies in the Western world.

In his lifetime, Pachelbel was renowned for his organ and other keyboard music, whereas today he is also recognized as an important composer of church and chamber music. Little of his chamber music survives, however. Only Musikalische Ergötzung—a collection of partitas published during Pachelbel's lifetime—is known, apart from a few isolated pieces in manuscripts. The Canon and Gigue in D major is one such piece. A single 19th-century manuscript copy of them survives, Mus.ms. 16481/8 in the Berlin State Library. It contains two more chamber suites. Another copy, previously in Hochschule der Künste in Berlin, is now lost.

The circumstances of the piece's composition are unknown. Hans-Joachim Schulze, writing in 1985, suggested that the piece may have been composed for Johann Christoph Bach's wedding, on 23 October 1694, which Pachelbel attended. Johann Ambrosius Bach, Pachelbel, and other friends and family provided music for the occasion. Johann Christoph Bach, the oldest brother of Johann Sebastian Bach, was a pupil of Pachelbel. Pachelbel scholar Kathryn Jane Welter considers this "pure speculation". Another scholar, Charles E. Brewer, investigated a variety of possible connections between Pachelbel's and Heinrich Biber's published chamber music. His research indicated that the Canon may have been composed in response to a chaconne with canonic elements which Biber published as part of Partia III of Harmonia artificioso-ariosa. That would indicate that Pachelbel's piece cannot be dated earlier than 1696, the year of publication of Biber's collection. Other dates of the Canon's composition are occasionally suggested, for example, as early as 1680.

The canon (without the accompanying gigue) was first published in 1919 by scholar Gustav Beckmann, who included the score in his article on Pachelbel's chamber music. His research was inspired and supported by early music scholar and editor Max Seiffert, who in 1929 published his arrangement of the "Canon and Gigue" in his Organum series. That edition contained numerous articulation marks and dynamics not in the original score. Furthermore, Seiffert provided tempi he considered right for the piece, but that were not supported by later research. The canon was first recorded in Berlin in 1938 by Hermann Diener and His Music College, under the title, "Dreistimmiger Kanon mit Generalbass."

In 1968, the Jean-François Paillard chamber orchestra made a recording of the piece that would change its fortunes significantly. This rendition was done in a more Romantic style, at a significantly slower tempo than it had been played at before, and contained obbligato parts, written by Paillard. The Paillard recording was released in June in France by Erato Records as part of an LP record that also included the Trumpet Concerto by Johann Friedrich Fasch and other works by Pachelbel and Fasch, all played by the Jean-François Paillard chamber orchestra. Paillard's interpretation of the canon was also included on a widely distributed album by the mail-order label Musical Heritage Society in 1968.

In July 1968, Greek band Aphrodite's Child released the single "Rain and Tears", which was a baroque-rock adaptation of Pachelbel's Canon. The band was based in France at the time, although it is unknown whether they had heard the Paillard recording, or were inspired by it. "Rain and Tears" was a success, reaching number 1 on the pop charts of various European countries. Several months later, in October 1968, Spanish band Pop-Tops released the single "Oh Lord, Why Lord", which again was based on Pachelbel's Canon. Again, it is unknown whether they were aware of or had been inspired by the releases from earlier that year. "Oh Lord, Why Lord" was covered by American band Parliament on their 1970 album Osmium.

In 1970, a classical radio station in San Francisco played the Paillard recording and became inundated by listener requests. The piece gained growing fame, particularly in California. In 1974, London Records, aware of the interest in the piece, reissued a 1961 album of the Corelli Christmas Concerto performed by the Stuttgart Chamber Orchestra, which happened to contain the piece, now re-titled to Pachelbel Kanon: the Record That Made it Famous and other Baroque Favorites. The album was the highest-selling classical album of 1976. Its success led to many other record labels issuing their own recordings of the work, many of which also sold well.