Katok or Katok Dorjeeden is one of the six principal monasteries of Nyingmapa sect of Tibetan Buddhism. Katok Monastery was founded in 1159 by a younger brother of Phagmo Drupa Dorje Gyalpo, Katok Dampa Deshek, at Derge, the historic seat of the Kingdom of Derge in Kham.
Katok Monastery held a reputation of fine scholarship. Prior to the annexation of Tibet in 1951, Katok Monastery housed about 800 monks.
Katok was long renowned as a center specializing in the oral lineages and as a center of monasticism, although both of these features were disrupted under Longsel Nyingpo (1625–1692).
Katog has 112 branch monasteries, not only in Tibet, but also in Mongolia, Inner China, Yunnan, and Sikkim. For instance, Katog Rigdzin Tsewang Norbu (1698-1755) founded a large branch in Sikkim, and when the Eighth Tai Situ Rinpoche, Situ Panchen Chokyi-jungney (1700-1744), visited China, he stayed at the Katog branch-monastery at the Five-Peaked Mountain of Manjushri Ch: Wutai Shan), to the southwest of Beijing.