Yom Kippur is the holiest day of the Jewish year and is observed on the 10th day of the lunar month of Tishri, which usually falls in September or October. It is the final day of the ten-day period of repentance and reflection known as the "High Holidays," which begins with Rosh Hashanah. The purpose of Yom Kippur is to effect individual and collective purification by the practice of forgiveness of the sins of others and by sincere repentance for one’s own sins against God.

Yom Kippur is a day of private introspection and powerful communal connection. Jews traditionally fast on Yom Kippur, refraining from both food and drink for the entire 25 hours of the holiday. It is also traditional to refrain from other earthly pleasures, such as bathing and wearing leather shoes, something seen as a luxury in ancient times. Many Jews choose to wear white, symbolizing purity and renewal as they repent for their past sins.

The holiday is typically celebrated with a day of reflection, prayer, and fasting. Most Jewish people have a meal with lots of meat for lunch on the day before Yom Kippur, followed by a "Seudat Mafseket," or Meal of Cessation, for dinner, which is rich in carbohydrates and low in sodium. The biggest challenge during the fast is dehydration, so it is recommended to drink lots of water before the fast and prepare for the day-long fast up to a week in advance.

Yom Kippur begins with the Kol Nidrei service, which is a declaration annulling all vows made during the course of the year insofar as they concern oneself. The services on Yom Kippur itself last continuously from morning to evening and include readings from the Torah and the reciting of penitential prayers. Yizkor, which are memorial prayers for the recently deceased, may also be recited by members of the congregation. The services end with closing prayers and the sounding of the shofar, which indicates that God’s forgiveness has been granted and that the 25-hour fast is over.