Neoplatonism is a philosophy based on the ideas of Plato the Greek as interpreted primarily through Plotinus, an Egyptian Neoplatonist and student of Ammonius Saccas. His book The Enneads lays down some fundamentals, and the introduction written later by his student Porphyry further developed his ideas. Plotinus's influence extends to Proclus Lycaeus and Iamblichus, both of whom built on the foundation of his ideas and added Magical theories to them.
This was not the only Philosophical school at the time, and Zosimos of Panopolis, for example, was much more influenced by early Christianity, Persian astronomy and Aristotle than by Plato. His followers were much more likely to collect information and experiment, while Neoplatonists spent their efforts examining the Inner World, deducing and seeking it's unifying principles.
A great effort was made in Neoplatonism to reconcile Hebrew and Greek metaphysics and philosophy. Egyptian religion, to the extent they understood it, also plays a role. The exile of the Soul into a body, it's life, and eventual return to the ONE remains the main goal, while techniques vary considerably. Like Gnosticism, it views this world and this body more as a prison for the Soul than its reward or proving ground. Unlike Gnosticism, it does not think the world is ruled by an Evil Demi-God. Rather Creation is the unaware fruit of God's process, made up of HIS substance. Both believe the Soul forgets its True Self upon birth, and must spend this life time recovering that connection.
Interest was renewed in Renaissance Italy, where Marsilio Ficino and his student Giovanni Pico della Mirandola translated the Greek for Italian audiences, incorporated Qabalistic cosmology, Memory techniques and added theory about the life force energy. Rudolf Steiner's techniques have a strong Neoplatonist basis, as do some of the Magickal techniques taught by Eliphas Levi and The Hermetic Order of the Golden Dawn.
Comments: Gnostic; Ancients; The Theory of the One, or the Creation Theory of the Qabalists; See also: Leucippus (theory of the Atom) ;Hypatia of Alexandria; Hierocles of Alexandria ; Olympiodorus the Younger; Simplicius of Cilicia; Thales; and for later development, Moses Maimonides; St. Augustine of Hippo;