Tarquinio Merula (1594 or 1595 – 10 December 1665) was an Italian composer, organist, and violinist of the early Baroque era. Although mainly active in Cremona, stylistically he was a member of the Venetian school. He was one of the most progressive Italian composers of the early 17th century, especially in applying newly developed techniques to sacred music.

He was born in Busseto. He probably received early musical training in Cremona, where he was first employed as an organist. In 1616 he took a position as organist at S Maria Incoronata in Lodi, where he remained until 1621, at which time he went to Warsaw, Poland to work as an organist at the court of Sigismund III Vasa.

In 1626 he returned to Cremona, and in 1627 became maestro di cappella at the cathedral there, but he only remained for four years, moving to Bergamo to accept a similar position in 1631. Alessandro Grandi, his predecessor, had died in the terrible plague of 1630 (which affected many cities in northern Italy, including Venice), and he faced the formidable task of rebuilding the musical institution there after many of its members had died.

Unfortunately Merula got into trouble with some of his students, and was charged with indecency; he chose to return to Cremona, where he remained until 1635. During this period in his life he seems to have had numerous troubles with his employers, possibly of his own making; after fighting with the administrators at Cremona over a variety of issues, he returned to Bergamo, serving this time at a different church, but was disallowed from using any musicians from his former place of employment. In 1646 he went back to Cremona for the final time, serving as maestro di cappella at the Laudi della Madonna until his death in 1665.

Merula was a key figure in the early development of several forms which were to mature later in the Baroque era, such as the cantata, the aria, the sonatas da chiesa and da camera, variations on a ground bass, and the sinfonia.

In sacred music Merula followed the lead of Monteverdi, and often used the techniques of the elder composer; however he also did some new things, such as writing motets for solo voice accompanied by strings. His publications of 1639, 1640, and 1652 include masses which are written using ostinato basses, including the Ruggiero and the Romanesca. Some of his music is reminiscent of the concertato style of Giovanni Gabrieli, and a modern sense of tonality prevails throughout.

Merula's secular music includes solo madrigals with instrumental accompaniment, sometimes using the Monteverdian stile concitato tremolo effect, and in formal design prefiguring the later Baroque cantata with its division into aria and recitative. He wrote one opera, La finta savia, produced in 1643, and based on a libretto by Giulio Strozzi. Among his instrumental music are numerous ensemble canzonas, whose sectional structure looks ahead to the sonata da chiesa, and his writing for strings—especially the violin—is exceptionally idiomatic, also looking ahead to the highly developed writing of the late Baroque.

He also wrote canzonettas, dialogues, keyboard toccatas and capriccios, a Sonata cromatica, and numerous other pieces which display an interest in just about every contemporary musical trend in north Italy.

A complete edition of his works was published in 1974 in Brooklyn, New York (T. Merula: Opere complete, ed. A. Sutkowski). A compilation of several of his solo vocal works was edited in 2012 by Phoebe Jevtovic, and samples can be found on her official website.