Between the 17th of Tammuz and Tisha B'av
1. Since the calamities accompanying the [Temple's] destruction began on
the Seventeenth of Tammuz, certain aspects of mourning are observed from
this day until after Tish'ah B'av ("ninth of Av"). It is appropriate that
every G-d-fearing individual recite the prayers of "Tikkun Chatzos" at
midnight during these days.
One may not marry [during this three week period]. This applies even to an
individual who has not fulfilled the mitzvah of procreation. [A couple]
is, however, permitted to become engaged ("la'asos shiduchin") (1) and even
[to celebrate the engagement] with a meal, until Rosh Chodesh Av (first day
of Av). From that date onwards (until Tish'ah B'av), although a couple may
become engaged (2), they should not celebrate with a meal (3). They may,
however, serve pastries and the like.
A Jew who is employed as a musician is permitted to play for gentiles to
earn his livelihood until Rosh Chodesh. From Rosh Chodesh until after the
fast [of Tish'ah B'av], however, this is forbidden. Similarly, it is
forbidden to do so on the Seventeenth of Tammuz itself, and also on the
Tenth of Teves.
Some people follow the custom of not eating meat or drinking wine from the
Seventeenth of Tammuz until after Tish'ah B'av, except on Shabbos (4) or at
a meal associated with a mitzvah (5).
(1) Even actual "kiddushin," that is, the first step which legally binds
the bride to the groom, is permissible.
(2) Kiddushin can take place even on Tisha B'av itself, because the Sages
were concerned that if we force a couple to postpone an engagement, the
bride may accept a marriage proposal from someone else (Mishna Berura 551:17).
(3) They may not hold this celebratory meal, even on Shabbos.
(4) It is not permissible to refrain from eating meat and drinking wine on
Shabbos as an expression of mourning (Ibid. 59).
(5) The most predominant custom among ashkenazim is to refrain from eating
meat and drinking wine from the first day of Av until after Tisha B'av.