Born in Bitchu province (modern-day Okayama), Eisai started his studies of Buddhism in a Tendai temple. Dissatisfied with the state of Buddhism at the time, in 1168 he set off on his first trip to Mt. Tiantai, the home of the sect, where he first encountered Chan (later known in Japan as Zen) ideas. He spent only half a year in China this time, but returned in 1187 for a longer stay as a disciple of Xuan Huaichang.
After his certification as a Zen teacher, Eisai returned Japan in 1191, bringing with him Zen scriptures and tea seeds. He immediately founded the Hoonji Temple in remote Kyushu, Japan's first Zen temple.
Eisai set about slowly propagating the new faith, trying to gain the respect of both the Tendai school and the Imperial court through careful diplomacy. Faced with the opposition of traditonal schools of Buddhism such as Tendai, Shingon and Pure Land, Eisai finally left Kyoto for the north-east to Kamakura in 1199, where the Shogun and his warrior caste of Samurai enthusiastically welcomed his martial-arts-oriented Zen teachings. Hôjô Masako, the widow of Yoritomo, allowed him to build Jufukuji, the first Zen center in Kamakura.
Eisai died in 1215 at the age of 75. His disciple Dogen went on to found the Soto school of Zen in Japan.
Eisai himself may have regarded some expressions of his thought as impure because they were necessarily compromised due to political considerations.
In Eisai, then-at least in the little preface to his major work-we stand in the presence of systematics on the part of a man whose whole tradition is noted for its claim to transcend of even eliminate systematics.
The importance for Eisai of active mind and heart (kokoro) is seen in Eisai's giving a copper halo to a poor man, in his mode of justifying that action and, finally,in his extolling kokoro not only as the all-embracing reality but as the source of Primal Energy.
Eisai set about slowly propagating the new faith, trying to gain the respect of both the Tendai school and the Imperial court through careful diplomacy.