The Book of Judith is a deuterocanonical book, included in the Septuagint and in the Roman Catholic and Eastern Orthodox Christian Old Testament of the Bible, but excluded by Jews and Protestants. It has been said that the book contains numerous historical anachronisms, which is why many scholars now accept it as unreliable history; it has been considered a parable or perhaps the first historical novel.

The name Judith ( , Yahūdīt) is the feminine form of Judah.

The Book of Judith has a tragic setting that appealed to Jewish patriots and it warned of the urgency of adhering to Mosaic Law, generally speaking, but what accounted for its enduring appeal was the drama of its narrative.

The story revolves around Judith, a daring and beautiful widow, who is upset with her Jewish countrymen for being unwilling to engage their foreign conquerors. She goes with her loyal maid to the camp of the enemy general, Holofernes, to whom she slowly ingratiates herself, promising him information on the Israelites. Gaining his trust, she is allowed access to his tent one night as he lies in a drunken stupor. She decapitates him, then takes his head back to her fearful countrymen. The Assyrians, having lost their leader, disperse, and Israel is saved. Though she is courted by many, she remains unmarried for the rest of her life.

As a historical tale, its scenes are enlivened and given immediacy by their setting in a definitely characterized (though anachronistic) setting and time, and connected, as all historical novels are, with important personages of history  here "Nebuchadnezzar" as a "King of Assyria" who reigns in Nineveh  features it shares with the Book of Esther, the Book of Daniel and its continuations, and the Book of Tobit. Nowhere are the "historical" details introduced in more profusion than in Judith.

With the very first words of the tale, "In the twelfth year of the reign of Nebuchadnezzar, who reigned over the Assyrians in Nineveh," it is argued by the compilers of the Jewish Encyclopedia that the narrator sets his story in "Once upon a time".

The city called "Bethulia," (properly "Betylua") and the narrow and strategic pass into Judea that it occupies (Judith IV:7ff VIII:21-24) are believed by many to be fictional settings, but some suggest that a city called Meselieh is Bethulia.

The editors of the Jewish Encyclopedia identified Holofernes' encampment with Shechem. The Assyrians, instead of attempting to force the pass, lay siege to the city and cut off its water supply. Although Nebuchadnezzar conquered Judah in reality, he is foiled in the narrative of the Book of Judith.

The Book of Judith was originally written in Hebrew. Though its oldest versions have been translated into Greek and have not been preserved in the original language, its Hebrew origin is revealed in details of vocabulary and phrasing. The extant Hebrew language versions, whether identical to the Greek, or in the shorter Hebrew version which contradicts the longer version in many specific details of the story, are medieval.