This codex, dated to the early fifth century C.E., originally contained the whole Bible in Greek. From the 11th century to the 17th century (1627), it belonged to the collection of the patriarch of Alexandria, Egypt​—hence the name Codex Alexandrinus. The pages of this manuscript are of fine vellum, and the text is written in uncial script. (See MANUSCRIPTS; UNCIAL.) Of the estimated 820 original leaves in this codex, 773 have been preserved. The codex is presently found in four volumes that are kept at the British Library in London. The first three volumes contain the Septuagint text of the Hebrew Scriptures, and the fourth, the Christian Greek Scriptures.

This codex was one of the first early Greek manuscripts of the Bible to become available for scholarly study. Because of its age and quality, it is considered to be one of the most valuable manuscripts of both the Greek Septuagint text and the text of the Christian Greek Scriptures. As such, it is one of the key sources of modern Bible translations. Scholars have used this authoritative manuscript, along with Codex Sinaiticus and Codex Vaticanus, to identify and correct additions and scribal errors that were introduced into later Bible manuscripts.​—See study note on Lu 10:1 and App. A5.