The tradition of Gnosis has taken on innumerable forms throughout the centuries; one of those forms is popularly assumed to be the totality of Gnosis: a diverse and often conflicting collection of traditions loosely centered around the Mediterranean Sea many centuries ago. Here are some example writings from that time and place, and an illustration of the true nature of the Gnostic teachings, which is far more ancient and wide-spread than humanity realizes, and is very much alive today.
This website has many articles and lectures that explain the most famous and widely known Gnostic scriptures: the books of Moses and the Gospels of Christianity. Kabbalah of Genesis reveals many of the mysteries of the book of Genesis.
A one-sentence description of Gnosticism: a religion that differentiates the evil god of this world (who is identified with the god of the Old Testament) from a higher more abstract God revealed by Jesus Christ, a religion that regards this world as the creation of a series of evil archons/powers who wish to keep the human soul trapped in an evil physical body, a religion that preaches a hidden wisdom or knowledge only to a select group as necessary for salvation or escape from this world.
The term “gnostic” derives from “gnosis,” which means “knowledge” in Greek. The Gnostics believed that they were privy to a secret knowledge about the divine, hence the name. (Huxley coined “agnosticism” on the basis that all knowledge must be based on reason. We cannot rationally claim to have access to knowledge that is beyond the powers of the intellect.)