Philotheus of Sinai was a Christian monk and writer who lived in Egypt. He lived sometime before 1100 – most likely during the 9th century, or possibly the 10th century. Very little is known about his life.^[1]

Philotheus was the hegumen of Saint Catherine's Monastery (also known as the Monastery of the Burning Bush) in the Sinai Peninsula.^[1]

Philotheus of Sinai followed the Sinaitic ascetic tradition of John Climacus.^[1] His writings are similar to those of Hesychius of Sinai.^[2] These three monks of Sinai (namely John Climacus, Hesychius of Sinai, and Philotheus of Sinai) are often considered to form a single Sinaitic literary and religious tradition.^[3]

His 40 Texts on Watchfulness (Greek: νηπτικὰ κεφάλαια, romanized: nēptiká kephálaia) are included in the Philokalia.^[2]

• Nepsis (watchfulness)