The Book of Ruth (Hebrew: מגילת רות‎; Sephardic, Israeli Hebrew: [məɡiˈlat rut]; Ashkenazi Hebrew: [məˈɡɪləs rus]; Biblical Hebrew: Megilath Ruth "the Scroll of Ruth") is one of the books of the Hebrew Bible, Tanakh, or Old Testament. In the Jewish canon the Book of Ruth is included in the third division, or the Writings (Ketuvim). In the Christian canon the Book of Ruth is placed between Judges and 1 Samuel. It is a rather short book, in both Jewish and Christian scripture, consisting of only four chapters.

The full title in Hebrew is named after a young woman of Moab, the great-grandmother of David and, according to the Christian tradition, an ancestress of Jesus:מגילת רות, Megillat Ruth, or "the scroll of Ruth", which places the book as one of the Five Megillot. Goswell argues that while Naomi is the central character of the book, Ruth is the main character, and so the book "can be considered aptly named." The only other Biblical book bearing the name of a woman is the Book of Esther. The Book of Judith is not a part of the Jewish or most Protestant Bibles, who exclude the Book of Judith as apocryphal), though it is a part of the Catholic Bible.