Alfonso Fontanelli (15 February 1557 – 11 February 1622) was an Italian composer, writer, diplomat, courtier, and nobleman of the late Renaissance. He was one of the leading figures in the musically progressive Ferrara school in the late 16th century, and one of the earliest composers in the seconda pratica style at the transition to the Baroque era.
Fontanelli was born in Reggio nell'Emilia, the son of Count Emilio Fontanelli. His early musical education was with composer Gasparo Pratoneri, and he evidently showed a talent for writing as well; a number of his lyric poems survive.
He married for the first time in 1580, and in 1584 began his career as a courtier, statesman, and musician to the Este family in Ferrara. It was in the employ of the Este family that he first went to Rome in 1586; while there he probably met the renowned madrigalist Luca Marenzio, as well as members of the Roman school of composition, aspects of whose style appear in his music. His diplomatic activity while in Rome enhanced his reputation greatly, for in 1588 he received two honors: he was named "music counselor" to the Accademia de Parteni in Ferrara, and he was made a gentleman of the Ferrara court. He rose steadily in influence between then and its dissolution in 1597, when the ruling Este family was removed to Modena and the region of Ferrara was absorbed into the Papal States.
Fontanelli probably wrote most of his surviving compositions during the 1590s, and immediately after 1600. Not only was he active as a musician at the Ferrara court during the earlier part of this period, but he was active as a diplomat and statesman, traveling to the Gonzaga court in Mantua and the Medici in Florence, and mingling with local musicians in each place. In 1594 he traveled extensively with Carlo Gesualdo, going to Venice, Florence, Naples, and Venosa with the notorious composer and murderer. A correspondence from himself to his patron Alfonso II d'Este survives, containing much information on musical practice of the period. In 1591 Fontanelli's first wife died, and he married again, to Maria Biancoli, a marriage which was to prove troublesome.