Selichot

The recitation of Selichot — a series of penitential prayers and liturgy recited daily in preparation for the Days of Awe — reaches its climax with the recitation of the "Zechor Brit" ("Remember Your Covenant") Selichot on the day before Rosh Hashanah. (Click here for more about Selichot.)

This day's Selichot, which is slightly lengthier than the preceding days', is customarily said in the very early hours of the morning. In most synagogues, the Selichot are immediately followed by the morning prayers.

Click here for the Hebrew text of the Selichot.

Tachanun

Perhaps counter-intuitively, the tachanun (confessional sections of the prayers) is omitted from the day's morning prayers, as is done on all festive dates on the Jewish calendar. After all, it is the day before a holiday, and we are confident and certain that G‑d will judge us favorably and bless each and every one of His children with a sweet and happy new year!

When Satan sees that we are so confident, he loses confidence in his carefully prepared case

Shofar-less

The shofar is not sounded on the day before Rosh Hashanah (as it is every day throughout the previous month of Elul), to separate between the shofar soundings of the month of Elul — which are a minhag, or "custom" — and the Rosh Hashanah soundings, which are a biblically ordained mitzvah.

Another reason given for not sounding the shofar on this day is in order to confuse Satan, the supernal prosecutor, as he prepares his case against us for tomorrow's Day of Judgment. The blowing of the shofar is a great weapon in our arsenal, as it is symbolic of the horn of the ram which was sacrificed in stead of Isaac, and thus evokes the merit of our holy Patriarchs and the sacrifices they made out of their deep love for G‑d. When Satan sees that we are so confident that we will be victorious on the Day of Judgment that we don't even find it necessary any more to sound the shofar, he is utterly confounded and loses confidence in his carefully prepared case.

Annulment of Vows

After the morning prayers, it is customary to perform a ceremony known as Hatarat Nedarim ("the annulment of vows") to repeal certain vows which one has taken upon oneself so that one can begin the Day of Judgment free from the sin of unfulfilled vows.

Certain vows which one has accepted upon oneself can, legally, be repealed by a court of three people. Many communities, including Chabad, have the custom of doing so before an assembly of ten individuals. The person approaches the panel and declares that he had possibly accepted vows upon himself, but had he known that he would be unable to fulfill them, he would never have accepted them upon himself. The person is then told three times that his vows are annuled.

It has become customary to recite the formula that is printed in the prayer books, for that formula describes in detail the various types of vows and the manner in which they can be repealed.

The basic hatarat nedarim procedure: four (or eleven) men convene. One of them stands up and faces the remaining panel of "judges," who are seated, and asks for them to annul his vows, which they do. That person then is seated, becoming part of the panel, and the next individual asks for annulment, and so on until all have had their vows annulled.

It is not customary for women to do hatarat nedarim.

(In Sephardic communities, it is customary to repeal one's vows twice each year: forty days before Rosh Hashanah, on the 19th of Av; and forty days before Yom Kippur, on the 1st of Elul.)