As we have explained (see this), on the 17th of Tamuz of the year 68 of the CE, after many months of siege, the walls of the city of Yerushalayim were destroyed by the Roman legions.
Once inside, the invading army pillaged the Holy City and thousands of Jews were killed, tortured or taken as slaves. The Bet haMiqdash was destroyed and burned three weeks after the Romans enter the city, on the 9th of Ab. Six hundred years earlier, in 586 BCE, the first Bet haMiqdash was destroyed also on the 9th of Ab.
As we approach the 9th of Ab, considered the National day of Mourning of the Jewish People, we observe certain restrictions associated with mourning.
These restrictions become stricter as we get closer to the 9th of Ab.
These customs differ significantly from community to community.
We present here a few illustrations:
WEDDINGS: The Rabbis of the Talmud, Maimonides, Mara”n etc. did not mention any restrictions for celebrating weddings before the beginning of the month of Ab. For Sephardim, therefore, it is technically not forbidden to have a wedding ceremony between the 17 of Tamuz and the beginning of the month of Ab. The Ashkenazi custom, however, is to avoid wedding ceremonies from the 17th of Tamuz. In our days, maintaining a level of uniformity in this sensitive matter, Sephardic Jews also abstain from celebrating weddings during the three weeks.
SHEHEHEYANU: The Shulhan Arukh mentions that it is good to avoid eating a fruit of a new season, which will require the recitation of the blessing Sheheheyanu, during the three weeks. The custom for Sephardim (Rab Obadaia Yosef) and Ashkenazim (Penine Halakha) is to reserve this recitation of Sheheheyanu for Shabbat.
HAIRCUT: The custom for most Sephardim is to permit getting a haircut or shave until the week of Tish’a beAb. The Ashkenazi tradition (Ram”a 551:4) and the custom of some Moroccan and Algerian Jews as well, is different: haircut or shaving is forbidden from the 17 of Tamuz until after Tish’a beAb. (Haircut restrictions do not apply to women).