The '''Jesus Prayer''', also called the '''''Prayer of the Heart''''', the '''''Prayer of a Single Thought''''', or simply '''''The Prayer''''', is a short, simple prayer that has been widely used, taught and discussed throughout the history of [[Eastern Christianity]]. The exact words of the prayer have varied, from a simple form such as [[Kyrie eleison|"Lord, have mercy"]] to an extended form:

:"Lord Jesus Christ, Son of God, have mercy on me, the sinner."

It is, for the Orthodox, one of the most profound and mystical prayers and is often repeated endlessly as part of a personal [[asceticism|ascetic]] practice. There have been a number of [[Roman Catholic Church|Roman Catholic]] texts on the subject, but its usage has never achieved the same degree of devotion as in the Eastern Church. A more elaborate version known to some Roman Catholics by the same name goes: "O my Jesus, forgive us our sins, save us from the fires of Hell, and lead all souls to Heaven, especially those most in need of Your mercy."