A concerto is an instrumental work premised on a contrast between a single instrumentalist of small group of instrumentalists and a large, orchestral ensemble. This meaning has been applied with consistency since the 1700's, in contrast to the 1600's when there was a genre of sacred music referred to as chorale concertos. Most often it refers specifically to a work with three movements, the first and last being fast, while the middle is slow for either one soloist and orchestra, for multiple soloists and orchestra in a specialize version called the concerto grosso, or groups in an orchestra that is not divided.
The first concerti to appear in print were the six concerti a Quattro of Giuseppe Torelli in 1692. More important were his concerti musicali a Quattro op. 6 in which Torelli explains the significance of the word solo used for decorative passages to be played by a single instrument. As a result, he is sometimes identified as the inventor of the concerto form.
Two kinds of concertos developed: Roman and north Italian. The orchestra in Rome was formed a around a core group of players called the concertino, which comprised the players required for a trio sonata, balanced with a larger group called concerto grosso or ripieno. This shaped the Roman concerto around four separate violin parts and developments were in keeping with the sonata tradition. Arcangelo Corelli’s concertos were of this style.
In northern Italy, the concerto a cinque is formed around a principal violin, along with two more violins, a viola, and a cello, which may be doubled by a continuo, or alternatively, have a separate continuo part. Tomas Albinoni of Venice was markedly important in developing this style of concerto with his op. 2 and his Concerti a cinque op. 5.
Other composers who helped shape the concerto include Antonio Vivaldi, Johann Sebastian Bach, and Wolfgang Amadeus Mozart. Vivaldi wrote 500 or so concerti, of which the most famous are undoubtedly the solo violin concertos called Le Quattro stagioni — The Four Seasons in English: La primavera, L’estate, L’autunno, and — Spring, Summer, Fall, and Winter, which are program music.
Bach’s best known of his concerti are the six Brandenburg Concertos, originally titled Six Concerts Avec plusieurs instruments and completed in 1721. Bach varies the solo group, including not only violins, but also the piccolo violin, horn, oboe, bassoon, trumpet, recorder, harpsichord, and flute.
Mozart is known for his concertos for bassoon, oboe, flute, horn, piano, and his Clarinet Concerto in A Major. Other famous concerto composers include Ludwig van Beethoven, Johannes Brahms, Antonin Dvorak, Edward Elgar, Josef Haydn, Felix Mendelssohn, Sergei Rachmaninoff, Pyotr Il’yich Tchaikovsky, and Georg Telemann.