According to Sephardic custom, Selichot, special penitential prayers are said every morning during Elul. In this way the Sephardim recite Selichot for a period of 40 days, paralleling the 40 days Moses spent on Mount Sinai. Following each day of Elul, excluding Shabbat, the shofar is blown at the end of the service. The prevalent Ashkenazi custom is to recite Selichot for at least four days beginning on the Sunday prior to Rosh Hashanah or on the preceding Sunday if Rosh Hashanah is on Monday or Tuesday, as it is this year. For Ashkenazim, the first Selichot are recited late Saturday evening usually around midnight, and every morning thereafter, except Shabbat and Rosh Hashanah, until Yom Kippur, prior to the daily Shacharit service.

Selichot prayers are mentioned in the Mishnah, the codex of laws compiled around 200 C.E. by Rabbi Judah Ha-Nasi (R. Judah the Prince), and which come to be recognized as an authoritative statement of the Oral Law. Selichot originated as prayers for fast days, several of which happened in preparation for Rosh Hashanah. Although the poems recited may change from place to place and from tradition to tradition, the basic structure of the prayer service remains the same. The pattern of the penitential prayers is fixed and includes piyyutim (liturgical poems), differing each day, selected biblical verses, the Thirteen Attributes and a short confessional.

The prayers and hymns of the Selichot liturgy are structured around the recurrent recitation of the Thirteen Attributes of Mercy (shelosh esreh middot harahamim) from Shemot - Exodus 34:6-7. A minyan should be present for the recitation of the Thirteen Attributes although the Mishnah Berurah states that an individual can recite alone if necessary by reciting it with the Torah trope. The section is recited while standing, the same as we do when we read the verses from the Torah on fast days.