In the ancient Buddhist cosmology, the earth is not the only world, and human are not the only living beings. There are Three Worlds containing a total of thirty-one realms; and existence in every realm is temporary. Rebirths take place in any realms according to one’s karma, wholesome and unwholesome actions.

一切众生从无始以来，即已在六道中轮回不息。 一切有情生命，不仅是人畜，且有人所不能见的有情。佛陀概括世间一切有情众生为六大种类：即天、阿修罗、人、饿鬼、畜生、地狱。前三者属三善道，后三者属三恶道。