The thesis intends to provide a better understanding of the text and the background of the Valentinian treatise, Nag Hammadi Codex, I,5. The Introduction studies the manuscript (date and provenance, purpose, scribal signs, quality), the text (an anonymous and untitled treatise, originally written in Greek, representing the Oriental branch of Valentinianism, date most likely second half of the 3rd. cent. A.D.), the language (a form of Subachmimic, with numerous orthographic and grammatical peculiar ities). A brief survey of the system is also provided, where it is regarded from three different angles. The Translation is primarily meant as an attempt to elucidate the difficult, and inadequately understood, Coptic text, and as an index to the following Commentary. The Commentary discusses the translation and relates each passage to the treatise as a whole, and to the system it contains. Valentinian themes and technical terms are pointed out and analysed systematically. The broader religious and philosophical background for the ideas contained in the treatise have also been explored. A special effort has been made to relate the system of the treatise not only to Gnostic documents, Christian literature and Late Jewish material, but also to Philosophy, and in particular to the emanationist physics of Neopythagoreanism and Neoplatonism.