To the Western mind, Tibet has traditionally appeared as a remote yet uniquely fascinating country. Profoundly Buddhist in all aspects of its social, cultural, and religious life, it was, until 1959, dominated by a monastic hierarchy. In the imagination of some, the so-called Land of Snow (as the Tibetans style their country) has also been regarded as the home of mysterious, superhuman beings, mahatmas, who, from their secret abodes in the Himalayas, give mystic guidance to the rest of humanity.

As sources become more abundant, a more realistic and complex view of Tibetan history and religion is gaining ground. The following points, which make this clear, should be kept in mind.

First, Buddhism in Tibet is represented by several traditions, monastic "orders," or schools, which have certain basic traits in common but also differ in significant respects. This must be taken into account when reading written...