I don’t like to use the word incarnation because it may imply a preexisting psychic substance or soul, and Buddhism does not accept the existence of an eternal soul that incarnates. However, Buddhism believes in a stream of consciousness that gets transferred from one birth to the next. This stream of consciousness is an instance of mental occurrence, arising due to its own internal momentum as well as external stimuli, all of which seemingly perpetuate its continuity over time. It thus serves as the basis for one’s self-identity.

-- Traleg Kyabgon Rinpoche