The name “San Luigi dei Francesi” means Saint Louis of the French, and this church is France's national church in Rome.
It was built in the 1500s at the instruction of a Cardinal in the Medici family who would later become Pope Clement VII. Catherine de Medici had married the French king, contributed to the church's construction, and donated the land on which the church was built – further cementing the French connection. The Church of San Luigi dei Francesi occupies the site of a former church, Santa Maria, which was owned by the Medici family. It was begun in 1518 and consecrated in 1589. The interior is
all Baroque ornamentation, so there's no shortage of stuff to see, but the biggest attraction inside is the series of three St. Matthew paintings by Caravaggio. These paintings were commissioned for the church, so it's a great chance to see artwork in its original home rather than an art museum.
San Luigi dei Francesi is located near Piazza Navona and open Friday-Wednesday 10am-12:30pm and 3pm-7pm, Thursdays 10am-12:30pm. The church is free to enter, but you'll want to bring some coins to light up the fabulous Caravaggio paintings.