What is Tisha B'Av?

Answer 1

Tisha B'Av is the ninth day in the Jewish month of Av. This year it takes place from Monday 7/23rd at 8:00P.M. to Tuesday 7/24 at 8:45P.M. On this day we fast and mourn the destruction of both temples.
Additionally on Tisha B'Av, five national calamities occurred:

During the time of Moses, Jews in the desert accepted the slanderous report of the 10 Spies, and the decree was issued forbidding them from entering the Land of Israel. (1312 BCE)


The First Temple was destroyed by the Babylonians, led by Nebuchadnezzar. 100,000 Jews were slaughtered and millions more exiled. (586 BCE)
The Second Temple was destroyed by the Romans, led by Titus. Some two million Jews died, and another one million were exiled. (70 CE)
The Bar Kochba revolt was crushed by Roman Emperor Hadrian. The city of Betar -- the Jews' last stand against the Romans -- was captured and liquidated. Over 100,000 Jews were slaughtered. (135 CE)
The Temple area and its surroundings were plowed under by the Roman general Turnus Rufus. Jerusalem was rebuilt as a pagan city -- renamed Aelia Capitolina -- and access was forbidden to Jews.
Other grave misfortunes throughout Jewish history occurred on the Ninth of Av, including:
The Spanish Inquisition culminated with the expulsion of Jews from Spain on Tisha B'Av in 1492.
World War One broke out on the eve of Tisha B'Av in 1914 when Germany declared war on Russia. German resentment from the war set the stage for the Holocaust.
On the eve of Tisha B'Av 1942, the mass deportation began of Jews from the Warsaw Ghetto, en route to Treblinka.

Answer 2

It's a fast day in the Jewish calendar. It memorializes the destruction of the First Temple by the Babylonians and the Second Temple by the Romans.
It's the ninth day of the month of Av.

http://en.wikipedia.org/wiki/Tisha_B'Av

[oh, and this year it's on Tuesday, July 24th.- http://www.chabad.org/calendar/view/day.asp?tDate=7/24/2007 ]

Answer 3

It is the culmination of a period of mourning from the time the Jerusalem walls were breached (17 Tammuz) to the time the Temple was destroyed (9 Av.) It's a Yom Kippur style Yom Tov, fasting included. Pretty much everything terrible that happened to us, happened on 9 Av.

So we mourn. It's a typical Jewish "holiday"...except where the normal formula is "they tried to kill us, they failed, let's eat!" this one is, "they tried to devastate us, they won, let's...not eat."

It's very sad day, happening exactly 1 week from now, on July 24.

http://www.jewfaq.org/holidayd.htm

Answer 4

http://www.exodus2006.com/Tisha-B-Av.htm