Collegiata di San Tommaso, Baroque collegiate church in Castel Gandolfo, Italy.

The Collegiata di San Tommaso is a Baroque church with a Greek-cross plan, its arms twice as wide as they are long and covered by barrel vaults. The crossing is topped by a dome with a drum and lantern, decorated with eight stucco roundels of scenes from the life of Saint Thomas of Villanova and the Four Evangelists in the pendentives. The facade has a single portal with a semicircular pediment and a triangular gable bearing the papal coat of arms of Alexander VII.

Pope Alexander VII Chigi commissioned Gian Lorenzo Bernini to build a church at Castel Gandolfo as the palatine chapel of the adjoining papal palace. Work began in 1658 and lasted three years; the church was consecrated in 1661 after Antonio Raggi completed the interior stucco decoration. It was first intended for Saint Nicholas of Bari but was dedicated instead to Thomas of Villanova, canonized on 1 November 1658.

The church serves as a focal point for Castel Gandolfo's community, hosting regular religious services and local celebrations. It shapes the character of the town center and connects residents to their shared spiritual heritage.

The church stands in an extraterritorial zone that also covers the adjoining papal palace and villas, so it falls under the Vicariate of Vatican City rather than the Diocese of Albano. The facade faces the piazza; the iron bell tower with three bells is at the rear. The interior is best visited outside service times.

The stucco decoration inside was made by Antonio Raggi, not by Bernini, and was finished by 1661, when the church was consecrated. Bernini's design merges two dome systems: the coffered dome of the Pantheon and the ribbed, Brunelleschian dome of Florence Cathedral.