The Book of Esther (Hebrew: מְגִלַּת אֶסְתֵּר, romanized: Megillat Esther), also known in Hebrew as "the Scroll" ("the Megillah"), is a book in the third section (Ketuvim, כְּתוּבִים "Writings") of the Hebrew Bible. It is one of the five Scrolls (Megillot) in the Hebrew Bible and later became part of the Christian Old Testament. The book relates the story of a Jewish woman in Persia, born as Hadassah but known as Esther, who becomes queen of Persia and thwarts a genocide of her people.

The story takes place during the reign of King Ahasuerus in the Persian Empire. Queen Vashti, the wife of King Ahasuerus, is banished from the court for disobeying the king's orders. To find a new queen, a beauty pageant is held and Esther, a young Jewish woman living in Persia, is chosen as the new queen. Esther's cousin Mordechai, who is a Jewish leader, discovers a plot to kill all of the Jews in the empire by Haman, one of the king's advisors. Mordechai urges Esther to use her position as queen to intervene and save their people. Esther reveals her Jewish identity to the king and begs for mercy for her people. She exposes Haman's plot and convinces the king to spare the Jews. The holiday of Purim is established to celebrate the victory of the Jews of the empire over their enemies, and Esther becomes a hero to the Jewish people.

The books of Esther and Song of Songs are the only books in the Hebrew Bible that do not mention God. Traditional Judaism views the absence of God's overt intervention in the story as an example of how God can work through seemingly coincidental events and the actions of individuals.

The book is at the center of the Jewish festival of Purim and is read aloud twice from a handwritten scroll, usually in the synagogue, during the holiday: once in the evening and again the following morning. The distribution of charity to the needy and the exchange of gifts of foods are also practices observed on the holiday that are mandated in the book.