This day marks the end of the Ten Days of Penitence that began with Rosh Hashanah. It is described in Leviticus as a “Sabbath of rest,” and synagogue services begin the preceding sundown, resume the following morning, and continue to sundown.

Considered to be one of the holiest and most solemn days of the year, its central theme is atonement and reconciliation. Eating, washing, cosmetics, wearing leather shoes, and conjugal relations are prohibited. Total abstention from food and drink usually begins half-an-hour before sundown (called "tosefet Yom Kippur," the "addition" of fasting part of the day before is required by Jewish law), and ends after nightfall the following day. Although the fast is required of all healthy adults, fasting is specifically forbidden for anyone who might be harmed by it.

Yom Kippur is observed in different ways in different Jewish communities. Sephardic Jews (Jews of Spanish, Portuguese and North African descent) refer to this holiday as "the White Fast." Consequently, many Jews have the custom of wearing only white clothing on this day, to symbolize their "white" (pure) desire to free themselves from sin. Ashkenazic Jews, while acknowledging the origins of the holiday as a day of rejoicing, tend to take a more somber, solemn attitude to the day.