The most well known and authoritative document in the masorah (“transmission”) of the entire Hebrew Bible, written in codex (book) rather than scroll form. It was produced and edited by the influential masoretic scholar Aaron ben Asher in the 10th century c.e.. According to modern studies, the Codex comprises the most accurate representation of Masoretic principles in any extant manuscript, having very few errors among the millions of orthographic details that make up the Masoretic text. For this reason the Codex is viewed as the most authoritative source document for both the original biblical text and its vocalization (vowels and cantillation marks). Until recently it was the oldest complete manuscript of the Hebrew Bible; however, in 1947 it was lost when the synagogue that housed it was looted and burned. Some parts have been recovered, but approximately 40 percent of it, including nearly all of the Torah, remain lost.
The Codex was given to the Jewish community of Jerusalem after its completion in the 10th century. During the First Crusade it was among the items that were captured and held for ransom by the Crusaders. The elders of Ashkelon were able to gain control of it and the Codex was brought to Egypt together with a group of Jewish refugees. It eventually came to reside in the Rabbanite synagogue in Cairo, where Maimonides used it in making his own copy of the Torah and in formulating his rules for writing Torah scrolls. At the end of the 14th century, Maimonides’ descendants brought it to Aleppo, Syria, where it remained for five hundred years, until 1947, when Muslim anti-Jewish riots desecrated the synagogue in which it was kept. The Codex remained lost until 1958, when it was smuggled into Israel by a Syrian Jew, but parts of the Codex were missing. Since then, two additional folios (pages) of the Codex have been recovered, but more than a third of the work remains missing.

Before parts of the Aleppo Codex were lost (i.e., before 1947), the order of its books followed the Tiberian Masoretic textual tradition, similar to that of the Leningrad Codex. The books of the Torah and Nevi’im (Prophets) appeared in the same order found in most printed Hebrew Bibles; however, there are significant differences in the order of its books in Ketuvim (Writings)—the order in the Codex is: Chronicles, Psalms, Job, Proverbs, Ruth, Song of Songs, Ecclesiastes, Lamentations, Esther, Daniel, Ezra, Nehemiah.