This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book gives weight to the importance of understanding the ancient bases and inheritance of Gnostic thought and practice, and this gives necessary background to many essays on Gnostic currents and movements running to our time. It is high time scholars and general readers alike should have the opportunity to contemplate and probe "the Gnostic World" as a whole, guided by the best up-to-date scholarship. An immense amount of ink is still being spilt on interpreting the Gnostic texts of Antiquity, in particular the Nag Hammadi Codices in Coptic from the early Christian centuries, materials from Egypt ranking with Judaea's Dead Sea Scrolls among the most spectacular archeological discoveries ever. In the most general way gnosis implies a better than ordinarily accessible "knowledge," and a Gnostic in the generic sense would be someone who is a deep and wise knower.