There was originally an old medieval church on this spot dedicated to St Florenzio, an obscure 5th-century follower of St Martin of Tours. The Oratorians, founded by St Philip Neri in Rome in 1575, purchased it in 1640 and replaced it with a richly stuccoed Oratory designed by Pier Francesco Silvani. As the popularity of the congregation grew, a church was added to the north by Pietro da Cortona, although his original design was changed. Its single nave, with its richly gilded ceiling illuminated by clerestory windows, has three altars filled with lugubrious 17th and 18th century paintings.
Eventually the complex took up the whole side of Piazza San Firenze, and given its final unifying facade by Ferdinando Ruggieri in 1715.
After being suppressed and unsuppressed a couple of times in the 19th century, the church was rededicated jointly to the Immaculate Conception and San Filippo Neri, while the seminary was requisitioned for office space. It was expanded yet again in the 1860s, during the city's brief fling as Italy's capital. Repaired after damage in the floods of 1966, it was until 2015, used by Florence's law courts as well as the Oratorian Fathers; today it's home to the Fondazione Franco Zeffirelli.
Piazza San Firenze
Image by Sailko, GNU Creative Commons License