This church is dedicated to St. Ignatius Loyola, founder of the order, and is characteristic of the Counter-Reformation Jesuit style. In fact, it was a Jesuit, Orazio Grassi, who designed it. Its high, strict and solemn-looking facade overlooks the charming Piazza S. Ignazio.
The main vault is adorned with a fresco by Andrea Pozzo. This Jesuit theorist of three-dimensional perspective and a trompe-l'oeil virtuoso, painted over imaginary architecture. Here, a multitude of figures move around St. Ignatius, who is illuminated by divine light, which is reflected on the allegorical portrayal of the four parts of the world. A circle marked at the centre of the nave shows where to stand in order to get the best view of this fresco.
The tireless Andrea Pozzo also painted the apse fresco, as well as the trompe-l'oeil "dome" decorating the transept crossing.