, formally known as Tenryū Shiseizen-ji, is the head temple of the Tenryū-ji branch of the Rinzai sect of Zen Buddhism, located in Susukinobaba-chō, Ukyō Ward, Kyoto, Japan. The temple was founded by Ashikaga Takauji in 1339, primarily to venerate Gautama Buddha, and its first chief priest was Musō Soseki. Construction was completed in 1345. As a temple related to both the Ashikaga family and Emperor Go-Daigo, the temple is held in high esteem, and is ranked number one among Kyoto's so-called Five Mountains. In 1994, it was registered as a UNESCO World Heritage Site, as part of the "Historic Monuments of Ancient Kyoto".
In the early Heian period, Empress Tachibana no Kachiko, wife of Emperor Saga, founded a temple called Danrin-ji on the site of present-day Tenryū-ji. The temple fell into disrepair over the next four hundred years.
In the mid-thirteenth century, Emperor Go-Saga and his son Emperor Kameyama turned the area into an imperial villa which they called "Kameyama Detached Palace". The name "Kameyama", which literally means "turtle mountain", was selected due to the shape of Mt. Ogura, which lies to the west of Tenryū-ji—it is said to be similar to the shape of a turtle's shell. All Japanese temples constructed after the Nara period have a sangō, a mountain name used as an honorary prefix. Tenryū-ji's sangō, Reigizan, was also selected due to the shape of Mt. Ogura.
The palace was converted into a temple in the middle of the Muromachi period at the behest of Ashikaga Takauji, who wished to use the temple to hold a memorial service for Emperor Go-Daigo. Ashikaga became the shōgun in 1338, and Go-Daigo died in Yoshino the following year. Ashikaga opposed the failed Kenmu Restoration, which was started by Emperor Go-Daigo, and the emperor decreed that Ashikaga be hunted down and executed. When his former-friend-turned-enemy died, Ashikaga recommended that Zen monk Musō Soseki construct a temple for his memorial service. It is said that the temple was originally going to be named Ryakuō Shiseizen-ji, Ryakuō being the name of the reign of the emperor of the northern court at that time.