Trompe-l'œil is an artistic term for the highly realistic optical illusion of three-dimensional space and objects on a two-dimensional surface. Trompe l'œil, which is most often associated with painting, tricks the viewer into perceiving painted objects or spaces as real. Forced perspective is a related illusion in architecture.

Illusionistic ceiling painting, which includes the techniques of perspective di sotto in sù and quadratura, is the tradition in Renaissance, Baroque and Rococo art in which trompe-l'œil, perspective tools such as foreshortening, and other spatial effects are used to create the illusion of three-dimensional space on an otherwise two-dimensional or mostly flat ceiling surface above the viewer. It is frequently used to create the illusion of an open sky, such as with the oculus in Andrea Mantegna's Camera degli Sposi, or the illusion of an architectural space such as the cupola, one of Andrea Pozzo's frescoes in Sant'Ignazio, Rome. Illusionistic ceiling painting belongs to the general class of illusionism in art, designed to create accurate representations of reality.