Tisha B'Av Fast and Other Practices
Given the plaintive nature of the day, it is not surprising that Tisha B'Av is a day of fasting. With the exception of Yom Kippur, this is the only fast day that lasts from sundown to sundown. (All the other days of fasting begin in the morning and end at night.)
Tisha B'Av is the culmination of a three-week period of mourning that begins with the fast of the seventeenth day of Tammuz (which commemorates the first breach of the walls enclosing Jerusalem). This period has certain restrictions: weddings and parties are not permitted, people do not cut their hair or wear new clothing. From the first through the ninth of Av (except on Shabbat), observant Jews also abstain from meat and wine.
If Tisha B'Av should fall on a Saturday, Shabbat takes precedence. Therefore, the fast is postponed until Saturday night through sundown on Sunday. In such an event, you need not eliminate bathing altogether and may do so the following day (though not the following night).
The restrictions on Tisha B'Av are similar to those on Yom Kippur, but also incorporate certain practices associated with mourning. On this day, avoid the following:
Eating or drinking
Washing or bathing (though you may wash your fingers up to the knuckles)
Shaving or wearing cosmetics and lotions
Wearing leather shoes
Having sexual relations
Working (at least until noon) or doing any pleasurable activity
Smiling, laughing, having idle conversations, or greeting others
Sitting on regular chairs (instead, you should sit on a low stool or on the ground)
Studying the Torah (with the exception of certain subjects related to mourning, since the study of Torah is a joyful experience)
By fasting, carrying out traditional rituals of mourning, and attending prayer services that to some extent have been customized to reflect the gravity of the day, you create the milieu for remembering some infamous times in Jewish history. In this fashion, you strengthen the links with the Jews of the past.
Do not greet anyone on Tisha B'Av. If someone is unaware of this mitzvah and greets you, explain the law and why you do not respond, or simply reply in a low voice and with a somber demeanor.
Synagogue Services During Tisha B'Av
Following the typical evening Ma'ariv service, the congregation reads from the Book of Lamentations, where the prophet Jeremiah describes the destruction of the First Temple. In some congregations, the congregants sit on the floor during the reading. Following Lamentations, they recite prayers of mourning.
To give added emphasis to the unique nature of this day of mourning, it is customary to remove the curtain from the Holy Ark where the Torahs are kept and to drape the Ark in black. In some synagogues, the main lights are turned off and prayers are recited by candlelight. On the morning of Tisha B'Av, at Shacharit prayers, men do not wear tallit and tefillin. While small tzitzit are donned, no blessing is made.