The Four Principle Schools
1. Nyingma (ancient) School
2. Sakya (Scholastic) School
3. Kagyu (Oral Tradition) School
4. Gelug (Tradition of Virtue) School
The Nyingma (ancient) School of Tibetan Buddhism developed from teachings of Padmasambhava and remained the only form of Buddhism in Tibet for nearly two hundred years. Buddhismn suffered vigorous persecution in the mid-ninth century, and subsequently declined until the eleventh.
However, it enjoyed a renewal following the journey to Tibet of the great Indian master, Atisa, in 1042. As a result of his teachings, Sakya Monastery was established some thirty years later. Because it developed close links with the Mongol Empire, the Sakya School eventually became very powerful, its teachings greatly revered, and many monasteries were established.
The Tibetan, Marpa, journeyed to India in the mid-eleventh century and received the precious teachings of the great adept, Naropa, one of the eighty-four siddhas, or great adepts.
Returning to Tibet, Marpa mastered these teachings and spread them widely. His hundreds of disciples eventually formed the new Kagyu (Oral Tradition) School which later established monasteries and gave teachings to a widening circle in Tibet, Mongolia and China. Marpa's most important disciple was the great Milarepa, Tibet's most revered mystic poet and ascetic, who in turn had thousands of disciples, women and men.
The Gelug (Tradition of Virtue, sometimes known as the 'Yellow Hat') School came into being in the early fifteenth century as a result of the extraordinary insights of Tsongkhapa, who commenced his studies at the age of three. After spending some twenty years studying with Nyingma, Sakya, Kagyu and Kadam (Oral Instruction) teachers, he convened a great council to review monastic discipline, and this provoked a new wave of monastic renewal that affected all of Tibet. Towards the end of his life his disciples founded the three great Gelugpa monastic universities of Ganden, Drepung and Sera near Lhasa. The institutions and lineages of both the Panchen Lamas and the Dalai Lamas developed within the Gelug school.