The Monastery of Saint John the Theologian (also called Monastery of Saint John the Divine) is a Greek Orthodox monastery founded in 1088 in Chora on the island of Patmos. UNESCO has declared it a World Heritage site. It is built on a spot venerated by both Catholics and Eastern Orthodox as the cave where St. John of Patmos had visions.

In 1088, Byzantine Emperor Alexios I Komnenos gave the island of Patmos to the soldier-priest John Christodoulos. The greater part of the monastery was completed by Christodoulos three years later. He heavily fortified the exterior because of the threats of piracy and Seljuk Turks.

A total of 330 manuscripts are housed in the library (267 on parchment), 82 manuscript of the New Testament.