In this series, we have looked mainly at the current aspects of Earth, which means the four worlds as they exist at this moment. Our world — the fourth world — is the physical world in which we use our senses to see what does or does not exist. We are increasingly learning that other kinds of subtle energies and beings, and even worlds, also exist. The Sidhe and other human races, as well as beings such as dragons and unicorns, live in three of these worlds. We have seen that many other beings fulfill essential purposes in Earth’s system.