The observation of Tisha B’Av actually begins three weeks before with the 17th of Tammuz, a minor fast day itself.

Following this fast, a three week period of mourning is entered into.  No weddings are permitted to be held during his time. Nine days prior to Tisha B’Av, further restrictions are included: no haircuts are allowed, meat may not be eaten.

Tisha B’Av is a major fast day, beginning at sundown and ending at nightfall.  The synagogue is dimly lit and the mood is somber.  There are restrictions on putting on Tefillin, eating, drinking, marital relations, business related dealings, bathing, swimming and wearing leather.

Even the study of Torah, other than Lamentations, the Book of Job and certain other permitted texts is forbidden as Torah study is seen as a joyous pursuit.  As this is a day of mourning, observance requires sitting on a low stool.

Limited restrictions continue until midday on the 10th of Av because the First Temple was still burning.