The enormous influence of Aristotle's psychology has been always related to the reception and interpretation of his De Anima. The Paraphrase by Themistius, who ran his own philosophical school in Constantinople in the mid-fourth century, has been one of the most important texts in the Aristotelian tradition. This is mainly due to the influence of his interpretation of Aristotle's noetic on the great medieval thinkers, especially Averroes and Thomas Aquinas. That influence was also prominent on Renaissance Aristotelians and on later scholasticism. Themistius offered an interpretation of the account of the so called active intellect in the De Anima III.5 that rejected the identification of that intellect with God previously proposed by Alexander of Aphrodisias. But he also discussed other philosophical problems. His method was largely pedagogical. Themistius aimed to provide a clear restatement of Aristotle's textual basis which would be accessible as an elementary exegesis. To do so, he executed an interpretation of Aristotle's psychology that was faithful to the original text. But he was also aware of the need for some reconstruction and reformulation of those ideas that were far from being perfectly delimited by Aristotle himself in his text. This new critical edition is based on a thorough analysis of the manuscript tradition, which has been arranged and schematized by means of a stemma codicum. Medieval translations have also been considered, as well as the various printed versions of the text from the Aldine edition to the 19th century.