Nicholas Cabasilas (Greek: Νικόλαος Καβάσιλας; born 1319/1323 in Thessalonica; died 1392) was a Byzantine mystic and theological writer. Cabasilas is a saint within the Orthodox Church. His feast day is June 20. The Roman Catholic Church uses extracts from his Life in Christ as readings in the Liturgy of the Hours (Tuesday, Wednesday, and Thursday of the Fifth Week of Easter in Year II of the two-year cycle for the Office of Readings). He was on intimate terms with the emperor John VI Cantacuzene, whom he accompanied in his retirement to a monastery. He was once thought to have succeeded his uncle Nilus Cabasilas as archbishop of Thessalonica; however contemporary records of that see do not show Nicholas as serving in the capacity of archbishop. It is more likely that he served as a priest at the Manganon monastery near Constantinople. In the Hesychast controversy he took the side of the monks of Mount Athos and Saint Gregory Palamas. His chief work is his Περὶ τῆς ἐν Χριστῷ ζωῆς, ("On the Life in Christ"). in which he lays down the principle that union with Christ is effected by the three great mysteries of baptism, chrismation, and the eucharist. He also wrote homilies on various subjects, and a speech against usurers, printed with other works in Migne, Patrologia Graeca, c. i. A large number of his works is still extant in manuscript. Cabasilas' major works are Life in Christ and Commentary on the Divine Liturgy. These works display a profound understanding of the sacramental and liturgical life of the Eastern Orthodox Church and are accessible to and instructive for any Christian today worshiping in either the East or West.