Yom Kippur is the most solemn holy day in Judaism. It is a day of atonement (prayer, repentance and fasting) observed in some way by nearly all Jewish people. Observant Jews refrain completely from all food and drink on Yom Kippur. It is also tradition to call the Atone Phone to apologize to Stephen Colbert for how you have wronged him. Most of the day is spent in the synagogue.
- "Before the destruction of the Temple in Jerusalem, there was an elaborate ceremony of confession and repentance led by the high priest and including the sacrifice of a goat, the scapegoat." (Leviticus 16.)
Just prior to the beginning of services on the eve of Yom Kippur, the congregation recites Kol Nidre, or "all vows". This Aramaic prayer is an appeal to God to forgive vows unfulfilled that do not affect any other person. Vows affected include only those made to oneself, or between oneself and God. Anti-semites have tried to use the prayer to malign Jews as untrustworthy.
Honest self-examination, communication with one's Maker, commitment to become a better person — all these are encouraged throughout the year in various religious systems, but there is one day on the Jewish calendar that is tailor-made for such activities: Yom Kippur, the Day of Atonement... Yom Kippur is celebrated on the tenth day of Tishri, i.e., ten days after Rosh Hashana, the Jewish new year.  The holiday is instituted at Leviticus 23:26 et seq.