The Holy Monastery of Koutloumousiou is near Karyes, and is dedicated to the Transfiguration of the Saviour. The etymology of the name is in all probability connected with two phases in the life of the Monastery. A monastery with the name of Koutloumousi is mentioned in a document as early as 1169 and is to be identified with the one which bears that name today. Nevertheless, the second founder of the Monastery is thought to have been a certain Koutloumous, a member of a dynasty of the Seljuks converted to Christianity.
In the 4th century Koutloumousi passed through difficult times because of looting raids by the Catalans which set the seal on a process of weakening and decline which had begun as early as the 12th century. Prosperity came to the Monastery under the enlightened leadership of the Abbot Chariton of Imbros in the second half of the 14th century. Chariton obtained important help from John Vladislav in maintaining the privileges of the Greeks against the Romanians who had taken up residence there. In 1393 the Monastery was awarded the status of a stavropegic foundation. In the early 15th century monks from Koutloumousi took up residence in and annexed the deserted St Alypius Monastery. By a Patriarchal sigillium of 1428 the Alypius Monastery was absorbed by Koutloumousi, which thus became more powerful.
This period of prosperity was followed by one of decline, to which the great fire of 1497 contributed. In 1767 yet another fire destroyed the east wing of the Monastery. The assistance of the Patriarch of Alexandria Matthaios II was decisive for the Monastery's recovery. In the 19th century (1857 and 1870) fire again did serious damage to the buildings of Koutloumousi. Repairs were carried out through the efforts of the Abbot Meletios. The last fire occurred in 1980; the damage caused was recently made good.
The katholikon of Koutloumousiou dates from the 16th century and is a classic example of Athonite architecture. Its original wall-paintings have, however, been painted over. The phiale and the bell-tower are works of the 19th century. The Monastery possesses 18 kellia and the fine Skete of St Panteleimon (1790), with 22 kalyves. Of special artistic value is the carved wooden sanctuary screen. Koutloumousiou has seven chapels and an equal number outside its walls. The Chapel of the Mighty Protection has a wonder-working icon of Our Lady of the same name. The Monastery has in its safekeeping many relics of saints, vestments and interesting portable icons. The library contains 662 manuscripts and approximately 3,500 printed books. Koutloumousi holds sixth place in the hierarchy of Athonite monasteries and, like all the monasteries on Mount Athos today, is a coenobium. It has some 20 monks.