The laws of mourning during the Three Weeks, Nine Days and Tisha b'Av
The "Three Weeks" between the 17th of Tammuz and the Tisha B'Av have historically been days of misfortune and calamity for the Jewish people. During this time, both the First and Second Temples were destroyed, among other terrible tragedies.
These days are referred to as the period "within the straits" (bein hametzarim), in accordance with the verse, "All her oppressors have overtaken her within the straits" (Lamentations 1:3). On Shabbat, during the Three Weeks, the Haftorahs are taken from chapters in Isaiah and Jeremiah dealing with the Temple's destruction and the exile of the Jewish people.
During this time, various aspects of mourning are observed by the entire nation. We minimize joy and celebration. And, since the attribute of Divine judgement (“din”) is acutely felt, we avoid potentially dangerous or risky endeavors.

Aspects of mourning during The Three Weeks
  1. No weddings are held. (However, engagement ceremonies are permitted.)
  2. We do not listen to music.
  3. We avoid all public celebrations -- especially those which involve dancing and musical accompaniment.
  4. We avoid exciting and entertaining trips and activities. (Kaf HaChaim - OC 551:41)
  5. No haircuts or shaving. (Fingernails may be clipped up until the week in which Tisha B'Av falls.)
  6. We do not say the blessing She-hechianu on new food or clothes, except on Shabbat.
The Nine Days - an intensifying of mourning observances.
The period commencing with Rosh Chodesh Av is called the "Nine Days." During this time, a stricter level of mourning is observed, in accordance with the Talmudic dictum (Ta'anit 26), "When the month of Av begins, we reduce our joy."

1. We avoid purchasing any items that bring great joy.
2.  We suspend home improvements, or the planting of trees and flowers.
3.  We avoid litigation with non-Jews, since fortune is inauspicious at this time.
4.  We abstain from the consumption of meat (including poultry) and wine. These foods are symbolic of the Temple service, and are generally expressions of celebration and joy.
  • On Shabbat, meat and wine are permitted. This applies also to any other seuduat mitzvah -- for example, at a Brit Milah or at the completion of a tractate of Talmud.
  • Wine from Havdallah should be given to a child to drink.
5.  We refrain from wearing newly laundered garments, or laundering any clothes.
  • If the "freshness" has been taken out of a garment prior to the Nine Days, it may be worn.
  • Fresh clothes may be worn for Shabbat.
  • The clothing of small children, which gets soiled frequently, may be laundered during the Nine Days.
  • Clothes may not be laundered even if done in preparation for after Tisha B'Av, or even if done by a non-Jew.
6.  We do not bathe for pleasure.
  • It is permitted to bathe in order to remove dirt or perspiration, or for medical reasons. This may be done only in cool water.
  • Furthermore, the body should be washed in parts, rather than all at one time.
  • Bathing in warm water is permitted on Friday in honor of Shabbat.
What Happened on the Ninth of Av? Why is it a time of intense mourning?
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:
  1. The Spanish Inquisition culminated with the expulsion of Jews from Spain on Tisha B'Av in 1492.
  2. 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.
  3. On the eve of Tisha B'Av 1942, the mass deportation began of Jews from the Warsaw Ghetto, en route to Treblinka.
Aspects of mourning the afternoon before Tisha b'Av
During the afternoon prior to Tisha B'Av, it is customary to eat a full meal in preparation for the fast.
At the end of the afternoon, we eat the Seudah Hamaf-seket – a meal consisting only of bread, water, and a hard-boiled egg.
The egg has two symbols: The round shape reminds us of a sign of the cycle of life. Also, the egg is the only food which gets harder the more it is cooked – a symbol of the Jewish people's ability to withstand persecution. During the week of Shiva, the mourner traditionally eat these food items as well.
Food eaten at the Seudah Hamaf-seket, namely a boiled egg, is dipped in ashes, symbolic of mourning. The meal should preferably be eaten alone, while seated on the ground in mourner's fashion.
When the afternoon prior to Tisha B'Av occurs on Shabbat, there is no Seudah Hamaf-seket with eggs and ashes. Rather, the regular Shabbat "third meal" is eaten, albeit without guests and fanfare.
Restrictions on Tisha B'Av
Upon sundown, the laws of Tisha B'Av commence – consisting of the following expressions of mourning:
1. No eating or drinking until nightfall the following evening.
  • Pregnant and nursing women are also required to fast. If one suspects it could be harmful to the baby or mother, a rabbi should be consulted.
  • A woman within 30 days after birth need not fast.
  • Others who are old, weak, or ill should consult with a rabbi. (MB 554:11)
  • Medicine may be taken on Tisha B'Av, preferably without water.
  • In case of great discomfort, the mouth may be rinsed with water. Great care should be taken not to swallow anything. (MB 567:11)
2. Other prohibitions include:
  • Any bathing or washing, except for removing specific dirt – e.g. gook in the eyes (OC 554:9, 11). (Upon rising in the morning, before prayers, or after using the bathroom, one washes only the fingers. See OC 554:10, OC 613:3, MB 554:26)
  • Anointing oneself for pleasure. (Deodorant is permitted.)
  • Having marital relations.
  • Wearing leather shoes. (Leather belts may be worn.) (see: Laws of Shoes and Chairs)
  • Learning Torah, since this is a joyful activity. It is permitted to learn texts relevant to Tisha B'Av and mourning – e.g. the Book of Lamentations, Book of Job, parts of Tractate Moed Katan, Gittin 56-58, Sanhedrin 104, Yerushalmi end of Ta'anis, and the Laws of Mourning. In-depth study should be avoided. (MB 554:4)
3. Other mourning practices include:
  • Sitting no higher than a foot off the ground. After midday, one may sit on a chair. (OC 559:3)(see: Laws of Shoes and Chairs)
  • Not engaging in business or other distracting labors, unless it will result in a substantial loss. (OC 554:23)
  • Refraining from greeting others or offering gifts (OC 554:20)
  • Avoiding idle chatter or leisure activities
All information on the laws of mourning as well as the laws of observance for The Three eeks and Tisha b'Av were taken from the following two sites:
chabad.org
aish.com