Its paintings in the nave, crossing, and side chapels became models for art in Jesuit churches throughout Italy and Europe, as well as those of other orders.

Although the Council itself said little about church architecture, its suggestion of simplification prompted Charles Borromeo to reform ecclesiastical building practise.

There is no narthex in which to linger: the visitor is projected immediately into the body of the church, a single nave without aisles, so that the congregation is assembled and attention is focused on the high altar.

In place of aisles there are a series of identical interconnecting chapels behind arched openings,[b] to which entrance is controlled by decorative balustrades with gates.

The main door is well decorated with low relief, the papal coat of arms, and a shield with the initialism SPQR, tying this church closely to the people of Rome.

The main door stands under a curvilinear tympanum and over it a large medallion with the letters IHS representing the Christogram and an angel.

It was removed during the renovations in the 19th century and its tabernacle was subsequently purchased by archbishop Patrick Leahy for his new cathedral where it was installed after some minor modifications.

[10] The most striking feature of the interior decoration is the ceiling fresco, the grandiose Triumph of the Name of Jesus (1678-1679)[11] by Giovanni Battista Gaulli.

The ceiling is frescoed with the Glory of the Virgin surrounded by martyred saints Clemente, Ignazio di Antiochia, Cipriano, and Policarpo.

The third chapel to the right is the Cappella degli Angeli, which has a ceiling fresco of the Coronation of the Virgin and the altarpiece of Angels worshiping the Trinity by Federico Zuccari.

The larger Saint Francis Xavier Chapel, in the right transept, was designed by Pietro da Cortona, originally commissioned by Cardinal Giovanni Francesco Negroni.

The silver reliquary conserves part of the saint's right arm (by which he baptized 300,000 people), his other remains are interred in the Jesuit church in Goa.

[12] The first chapel to the left, originally dedicated to the apostles, is now the Cappella di San Francesco Borgia, the former Spanish Duke of Gandia, who renounced his title to enter the Jesuit order, and become its third "Preposito generale".

Pier Francesco Mola painted the walls, on left with St. Peter in jail baptizes saints Processo & Martiniano, to right is the Conversion of St. Paul.

The second chapel on the left is dedicated to the Nativity and called Cappella della Sacra Famiglia, commissioned by patron Cardinal Cerri who worked for the Barberini family.

In the roof, the Celestial celebration on the nativity of Christ, on the pinnacles are David, Isaiah, Zechariah and Baruch, on the right lunette an Annunciation to the Shepherds, and on the left a Massacre of the Innocents.

The third chapel to the left is the Cappella della Santissima Trinità, commissioned initially by the clerical patron Pirro Taro, named due to the main altarpiece by Francesco Bassano the Younger.

The reliquary on the altar holds the right arm of the polish Jesuit St. Andrew Bobola, martyred in 1657 and canonized by Pius XI in 1938.

The imposing and luxurious St. Ignatius Chapel with the saint's tomb is located on the left side of the transept and is the church's masterpiece, designed by Andrea Pozzo between 1696 and 1700.

Pope Pius VI had the original silver statue melted down, ostensibly to pay the war reparations to Napoleon, as established by the Treaty of Tolentino, 1797.

The name derives from a medieval icon, once found in a now-lost Church in the piazza Altieri, venerated by Saint Ignatius.

The painting depicting the death of Saint John Francis Regis by Jacopo Zoboli is located in the sacristy rooms.

Two ornamented façades flank the transept walls (Swell and Great on the left and Choir and Pedal on the right) and a small antiphonal division is located above the liturgical west entrance.