Judges 21 is the twenty-first (and final) chapter of the Book of Judges in the Old Testament or the Hebrew Bible. According to Jewish tradition the book was attributed to the prophet Samuel, but modern scholars view it as part of the Deuteronomistic History, which spans in the books of Deuteronomy to 2 Kings, attributed to nationalistic and devotedly Yahwistic writers during the time of the reformer Judean king Josiah in the 7th century BCE. This chapter records the war between the tribe of Benjamin and the other eleven tribes of Israel, belonging to a section comprising Judges 17 to 21.

This chapter was originally written in the Hebrew language. It is divided into 25 verses.

Some early manuscripts containing the text of this chapter in Hebrew are of the Masoretic Text tradition, which includes the Codex Cairensis (895), Aleppo Codex (10th century), and Codex Leningradensis (1008). Fragments containing parts of this chapter in Hebrew were found among the Dead Sea Scrolls including 4Q50 (4QJudg^b; 30 BCE–68 CE) with extant verses 12–25.

Extant ancient manuscripts of a translation into Koine Greek known as the Septuagint (originally was made in the last few centuries BCE) include Codex Vaticanus (B; ${\displaystyle {\mathfrak {G}}}$^B; 4th century) and Codex Alexandrinus (A; ${\displaystyle {\mathfrak {G}}}$^A; 5th century).

Chapters 17 to 21 contain the "Double Conclusion" of the Book of Judges and form a type of inclusio together with their counterpart, the "Double Introduction", in chapters 1 to 3:6 as in the following structure of the whole book:

There are similar parallels between the double introduction and the double conclusion as the following:

The entire double conclusion is connected by the four-time repetition of a unique statement: twice in full at the beginning and the end of the double conclusion and twice in the center of the section as follows:

It also contains internal links: