Ta'anit Esther, or the Fast of Esther is a Jewish fast day observed on the 13th of Adar (the 6th month of the Jewish calendar), which is the day before the Jewish holiday of Purim. This fast is observed to commemorate the fast observed by Esther, Mordechai, and the rest of the Jewish people on the days before Esther went to plead for the people of Israel before King Achashverosh. This fast is described in the Book of Esther as follows:

(Esther instructs Mordechai:) 'Go and gather all the Jews who are found in Shushan and fast over me, and do not eat and do not drink three days, night and day; and I and my maidens will also fast thus.' (Esther 4)

The fast was shortened by the Rabbis to be only one day instead of three, although some voluntarily observe a three-day fast. The Fast of Esther is a short fast, beginning before sunrise on the day of the fast instead of at sunset the evening before, like the fasts of Yom Kippur and Tisha B'Av.