Buddhist monasticism is an important part of the Tibetan Buddhist tradition, all the major and minor schools maintain large monastic institutions based on the Mulasarvastivada Vinaya (monastic rule) and many religious leaders come from the monastic community. That being said, there are also many religious leaders or teachers (called "Lamas" and "Gurus") which are not celibate monastics. According to Geoffrey Samuel this is where "religious leadership in Tibetan Buddhism contrasts most strongly with much of the rest of the Buddhist world."