The Codex Vaticanus (The Vatican, Bibl. Vat., Vat. gr. 1209; no. B or 03 Gregory-Aland, δ 1 von Soden), is one of the oldest extant manuscripts of the Greek Bible (Old and New Testament), one of the four great uncial codices. The Codex is named after its place of conservation in the Vatican Library, where it has been kept since at least the 15th century. It is written on 759 leaves of vellum in uncial letters and has been dated palaeographically to the 4th century.
The manuscript became known to Western scholars as a result of correspondence between Erasmus and the prefects of the Vatican Library. Portions of the codex were collated by several scholars, but numerous errors were made during this process. The Codex's relationship to the Latin Vulgate was unclear and scholars were initially unaware of the Codex's value. This changed in the 19th century when transcriptions of the full codex were completed. It was at that point that scholars realised the text differed significantly from the Vulgate and the Textus Receptus.
Current scholarship considers the Codex Vaticanus to be one of the best Greek texts of the New Testament, with the Codex Sinaiticus as its only competitor. Until the discovery by Tischendorf of the Sinaiticus text, the Codex was unrivaled. It was extensively used by Westcott and Hort in their edition of The New Testament in the Original Greek in 1881. The most widely sold editions of the Greek New Testament are largely based on the text of the Codex Vaticanus.