It is not unusual for an important Tibetan lama to be a trulku, or 'incarnate lama'. There are thought to be several thousand of them in contemporary Tibet. The abbots of many monasteries are trulku, and thus abbotship can be traced back through a lineage of rebirths to the original founder of the monastery, or at least to an important figure associated with the founding of the monastery.

Strictly speaking, however, this investiture of power through rebirth is known as yangsid, and a trulku is a manifestation of a Tantric deity that repeatedly expresses itself through a series of rebirths. The honorific title rinpoche, meaning 'very precious', is a mark of respect and does not necessarily imply that the holder is a trulku.

The most famous manifestation of a deity is of course the Dalai Lama lineage. The Dalai Lamas are manifestations of Avalokiteshvara, the Bodhisattva of Compassion. The Panchen Lama, on the other hand, is a manifestation of Manjushri, the Bodhisattva of Insight. There is no exclusivity in such a manifestation: Tsongkhapa, founder of the Gelugpa order, was also a manifestation of Manjushri, as traditionally were the abbots of the Sakya Monastery.

As a general rule, the reincarnations of high-status lamas tend to be found in aristocratic families (as in the early Dalai Lamas) or in families where trulkus have already been identified. The present Dalai Lama's family, for example, was by no means aristocratic, but his elder brother had already been identified as a trulku and his younger brother was also later recognised as a trulku.

Lamas approaching death often leave behind clues pointing to the location of their reincarnation. The Panchen Lamas have their reincarnation confirmed by lots drawn from a golden urn. Potential candidates are tested by picking out the lama's former possessions from a collection of objects. Disputes over trulku status are not uncommon. A family's fortunes are likely to improve if an incarnate lama is discovered among the children, creating an incentive for fraud.

It is possible to see in the trulku system a substitute for hereditary power (as in western royal lineages) in a society where many of the major players were celibate and unable to produce their own heirs. Not that celibacy was overwhelmingly the case. The abbots of Sakya took wives to produce their own trulku reincarnations, and it is not uncommon for rural trulkus to do the same.