The Askew Codex (a.k.a. Codex Askewianus) is a parchment manuscript in quarto size of 21 x 16,5 cm now held by the British Library (BL Additional MS 5114) which contains Coptic translations of the Gnostic Pistis Sophia and parts of what G. R. S. Mead referred to as "extracts from The Books of the Savior." It was purchased from the heirs of Dr. Anthony Askew by the British Museum (now British Library) in 1785. The origin is most probably from Egypt but it is not known where it was found or how this Manuscript ended up in England. The codex contains 178 leaves or 356 pages. The manuscript is in excellent condition but two leaves (pp. 337–344) are missing. The complete manuscript was written by two different hands. Both hands used different inks and different page numberings and a different way to mark corrections. Both writers seem to be of the same period.
Until the discovery of the Nag Hammadi library in 1945, the Askew Codex was one of three surviving codices containing all of the gnostic writings that had survived until recent times; the other two being the Bruce Codex and the Berlin Codex.