San Sebastian Church, Baroque church in central Madrid, Spain.

San Sebastian Church stands on Calle de Atocha, 39, in the old Barrio de las Musas. Its main volume is reddish-brown brick, divided into vertical bands by lighter stone pilasters and cornices, and topped by an octagonal brick tower with a small dome and cross. A small square bell tower with a dark arched opening projects from the side; the lower facade is smooth beige stone with tall arched windows and a dark wooden door. A grey slate dome with a lantern spire stands to the right.

The church was founded in 1541 as a chapel on the road to the Atocha shrine. The present building on Calle Atocha was raised from 1554 to 1575 under Antonio Sillero, with enlargements by Antonio de la Tijera and others between 1595 and 1598, and a tower by Lucas Hernández in 1612. Sacked and bombed in 1936, it was rebuilt with a changed orientation by Francisco Íñiguez Almech between 1943 and 1959.

The name comes from a devotional chapel (ermita) on the road to the Atocha shrine, founded in 1541. The actors' guild of the Virgen de la Novena was founded here on 24 July 1624, and the chapel of Nuestra Señora de la Novena was adopted by actors. The chapel of the Architects, to the right of the entrance behind a glass grille, holds the tombs of Ventura Rodríguez and Juan de Villanueva.

The church is located in Madrid's historic district with entrances on Calle Atocha and Calle Huertas. Access is primarily intended for religious services, so visitor hours may be limited.

The parish registers record the baptism of Ramón de la Cruz in 1731 and the wedding of Mariano José de Larra; a tile plaque at the entrance lists such entries. The cemetery behind the church, now the site of a flower shop, held Lope de Vega's remains and was where José Cadalso tried one night to dig up the body of his lover, the actress María Ignacia Ibáñez.