Theophilus is a prominent lunar impact crater that lies between Sinus Asperitatis in the north and Mare Nectaris to the southeast.

[2] Theophilus, Cyrillus and Catharina form a prominent group of large craters visible on the terminator 5 days after the new moon.

The rim of Theophilus has a wide, terraced inner surface that shows indications of landslips.

[5] The Apollo 16 mission collected several pieces of basalt that are believed to be ejecta from the formation of Theophilus.

[6] By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Theophilus.