We must remember that by the term ‘Jesus Prayer’ the Byzantine East refers, loosely enough, to any invocation centring in the Saviour's name itself. This invocation has taken various forms depending on whether it was used by itself, or included in more or less developed formulas. Moreover, it is for the individual to decide on his special way of invoking the name. In the East it has tended to take definite shape in the phrase 'Lord Jesus Christ, Son of God, have mercy on me a sinner', but this formula has not been, and is not, the only one. That is an authentic ‘Jesus Prayer’ in the Byzantine sense, which is a repeated invocation whose core and strength is the name of Jesus. One might say, for example, 'Jesus Christ', or ‘Lord Jesus'. The oldest formula, the simplest, and in our view the easiest, is the word ‘Jesus’ used by itself. It is in this sense that we shall speak here of the 'Jesus Prayer'.