THEOSIS Revised English Edition 2005
Archimandrite George Capsanis, the Abbot of Gregoriou Monastery on the holy mountain of Athos, has written a book which has been translated into english, and has been made (temporarily?) available on the website of Praxis Research Institute, who will also publish it.
Not everything on Praxis can be recommended, as the attempts to link the "esoteric Christianity" of various "fourth way" teachers (e.g. Gurdjieff, Ouspensky, Mouravieff etc.) to Athonite and Patristic spirituality by the institute, sometimes results in some odd readings of the Holy Fathers. They have, however, published two books by Archimandrite George, A translation of the Triads of St. Gregory Palamas and a book of sermons by St. Theophan the recluse which are generally good, with a few "caveat lectors".