Beginning at sunset on Tishri 9 and lasting until three stars appear after Tishri 10, Yom Kippur is the holiest day in the Jewish calendar. The observance is also known as the Day of Atonement since the events of Yom Kippur focus on asking and granting forgiveness for one's transgressions. Yom Kippur falls at the end of the ten Days of Penitence which begin with Rosh Hashanah, the Day of Judgment.
Jews attend services at a synagogue or temple on the eve and day of Yom Kippur. The Kol Nidre, a prayer which asks forgiveness of sins, is recited on the eve. Prayers which emphasize cleansing of the soul are recited during the day services. Congregants mourning family members who died in the past year recite Yiskor prayers in which God's forgiveness is asked for the deceased.
On Yom Kippur, Jews perform no work and abstain from food, drink, and sex. Laws about Yom Kippur are found in Leviticus 16, Leviticus 23:16-32, Leviticus 25:9, and in Numbers 29:7-11.