Answer:
   
   Jewish marriages do not take place on Shabbat, festivals or the High
   Holy Days, because "one does not mix one occasion of rejoicing with
   another." Weddings may be held on Chanukah and Purim, however, because
   they are not defined as a "simchah." Similarly, wedding are not
   traditionally held on days of public mourning either, for the
   overriding mood of such days would diminish the joy of the wedding.
   This includes Tisha B'Av, the fast of Gedaliah, the tenth of Tevet,
   the fast of Esther, the seventeenth of Tammuz,the period between
   Pesach and Shavuot, and the three weeks from the seventeenth of Tammuz
   until Tisha B'Av. The one exception is the thirty- third day in the
   Counting of the Omer (the period from Pesach through Shavuot), during
   which time weddings are permitted.
   
   This period also applies to the throwing of parties, such as
   engagement parties. However, there is an additional exception. If the
   "party" is really just a large Shabbat dinner, it is permitted,
   because public displays of morning do not take place on Shabbat. Note
   that, according to traditional thought, music should not be played
   during this period.