The Venetian polychoral style was a type of music of the late Renaissance and early Baroque eras which involved spatially separate choirs singing in alternation. It represented a major stylistic shift from the prevailing polyphonic writing of the middle Renaissance, and was one of the major stylistic developments which led directly to the formation of what is now known as the Baroque style. A commonly encountered term for the separated choirs is cori spezzati—literally, separated choirs.
The style arose from the architectural peculiarities of the imposing Basilica San Marco di Venezia in Venice. Aware of the sound delay caused by the distance between opposing choir lofts, composers began to take advantage of it as a useful special effect. Since it was difficult to get widely separated choirs to sing the same music simultaneously (especially before modern techniques of conducting were developed), composers such as Adrian Willaert, the maestro di cappella of St. Mark's in the 1540s, solved the problem by writing antiphonal music where opposing choirs would sing successive, often contrasting phrases of the music; the stereo effect proved to be popular, and soon other composers were imitating the idea, and not only in St. Mark's but in other large cathedrals in Italy. This was a rare but interesting case of the architectural peculiarities of a single building influencing the development of a style which not only became popular all over Europe, but defined, in part, the shift from the Renaissance to the Baroque era. The idea of different groups singing in alternation gradually evolved into the concertato style, which in its different instrumental and vocal manifestations eventually led to such diverse musical ideas as the chorale cantata, the concerto grosso, and the sonata.
The peak of development of the style was in the late 1580s and 1590s, while Giovanni Gabrieli was organist at San Marco and principal composer, and while Gioseffo Zarlino was still maestro di cappella. Gabrieli was the first to specify instruments specifically, including large choirs of brass; he also began to specify dynamics, and to develop the "echo" effects for which he became famous. The fame of the spectacular, sonorous music of San Marco at this time spread across Europe, and numerous musicians came to Venice to hear, to study, to absorb and bring back what they learned to their countries of origin. Germany, in particular, was a region where composers began to work in a locally-modified form of the Venetian style - most notably Heinrich Schütz - though polychoral works were also composed elsewhere, such as the many masses written in Spain by Tomás Luis de Victoria.
After 1603, a basso continuo was added to the already considerable forces at San Marco—orchestra, soloists, choir—a further step toward the Baroque cantata. Music at San Marco went through a period of decline, but the fame of the music had spread far, and transformed into the concertato style. In 1612 Claudio Monteverdi was appointed maestro di cappella, and though he brought the musical standards back to a high level, the vogue of the polychoral style had passed; concertato music, much with solo voice, was now the norm; the productions of this late period are identifiably Baroque.