Yūzū-nembutsu school 

One of the earliest schools of Pure Land Buddhism in Japan. The school was founded by Ryōnin (1072-1132), a monk of the Tendai school. He tried a variety of practices, including the nembutsu or contemplation of the Buddha Amitābha, but in the year 1117 he had a vision of Amitābha, who appeared before him and explained the philosophy of the yūzū-nembutsu, or ‘nembutsu of perfect interpenetration’ to him. The Buddha also revealed a maṇḍala to him that was to be his object of visualization. For several years, he kept this practice as his own, but in 1124 the deity Bishamonten appeared to him and implored him to teach this method of practice to the world. Thus, he left his quiet hermitage and went about, gathering followers and enlisting them in the practice.

The practice of the yūzū-nembutsu is based on Kegon (Chinese, Hua-yen) philosophy, which holds that all individual phenomena in the universe are interconnected and affect each other constantly. On this basis, Ryōnin asserted that a single person's recitation of the Buddha's name affected all other beings, rather than being a practice that aided only the practitioner. When two people recited the Buddha's name, then their efforts were interconnected, and the power to affect others multiplied. This concept had two effects in terms of the practice. First, it alleviated the need for the kind of strenuous, constant practice that was often given as the norm. If many people chanted the name, then the power of their practice combined and all benefited from the sum of their combined practice; this was opposed to the need for each individual to put forth heroic effort on their own behalf. Followers of Ryōnin could take on the burden of as few as 100 recitations of the name per day, rather than the 70,000 or more for which prior Chinese and Japanese masters were noted. Second, it gave a new twist to the idea of tariki, or ‘other-power’, which had previously been understood as the power of the Buddha Amitābha to bring about the rebirth of the individual. Under the yūzū-nembutsu, ‘other-power’ also included the cumulative power of all practitioners in addition to the power of the Buddha's vows.

Ryōnin was quite successful in enrolling members in a register, and possession of this book became the prerogative of the leader after his death. However, succession to the leadership lapsed after six generations, and the school went into a decline. The last abbot, Ryōchin, died in 1182 without a successor, and asked that the register be entrusted to the kami Hachiman, who would select the next leader. One hundred and forty years later, in 1321, Hachiman appeared to a prominent member named Hōmyō (1279-1349) in a dream, and named him the new leader. When Hōmyō reported this dream the next morning to the priests of the Hachiman shrine, they surrendered the register to him and he became the seventh abbot. Since Hōmyō had once been a Shingon monk, he was able to establish a special relationship between his school and the Shingon headquarters on Mt. Kōya, which led to the incorporation of the yūzū-nembutsu into Shingon practice. The school went into another decline after Hōmyō, especially because of the popularity of the newer Pure Land schools, the Jōdo Shū and the Jōdo Shinshū. It experienced another revival under the leadership of Daitsū (1649-1716). The school, though always small compared to other Japanese Pure Land schools, remains viable today.

A Dictionary of Buddhism, Oxford University Press, 2003, 2004 (which is available in electronic version from answer.com)