Gregory Palamas (Stanford Encyclopedia of Philosophy)
Stanford Encyclopedia entry on Gregory Palamas, the theologian who systematized hesychast theology and the distinction between God's essence and energies.
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Hesychasm (Orthodox Wiki)
Detailed overview of the Eastern Orthodox contemplative tradition of hesychasm, the Jesus Prayer, and inner stillness.
Christian Classics Ethereal Library
Free digital library of classic Christian texts including works by Meister Eckhart, John of the Cross, Teresa of Avila, and the Desert Fathers.
Mysticism (Stanford Encyclopedia of Philosophy)
Stanford Encyclopedia entry on mysticism with significant coverage of the Christian contemplative tradition.
On the Prayer of Jesus
Ignatius Brianchaninov
Classic guide to the Jesus Prayer practice and hesychast tradition by the 19th-century Russian bishop and spiritual writer.
The Philokalia
Collection of texts on contemplative prayer by Eastern Orthodox monks spanning the 4th to 15th centuries, central to the Hesychast tradition.