Tu B'Av (Hebrew: the fifteenth of the month Av) is a celebratory day in the Jewish calendar. The day has no special observances, but bears a mildly festive character, which is reflected in the omission of Tachanun, a downkey penitentiary prayer after the morning and afternoon prayer services.

The Talmud (tractate Taanit, fourth chapter) mentions Tu B'Av as a major festive day during the days of the Temple in Jerusalem, parallel in character to Yom Kippur: unmarried girls would lend each other simple clothes and sing and dance in the vinyards surrounding Jerusalem.

There are several reasons mentioned by the Talmud and its commentators:

• During the Jewish people's 40-year wandering in the desert, female orphans without brothers could only marry within their tribe, to prevent their father's inherited land in the Land of Israel to pass onto other tribes. On the fifteenth of Av of the fourtieth year, this ban was lifted.
• In the same year, the annual dying of participants in the Sin of Spies ceased.
• The Tribe of Benjamin was allowed to intermarry with the other tribes after the incident with the Concubine of Giv'ah.
• The wood offerings for the Temple ceased.
• The nights, traditionally the ideal time for Torah study, are lengthened again after the summer solstice, permitting more study.
• The Roman occupiers permitted burial of the victims of the Massacre of Bethar. It was discovered that - through a miracle - the bodies had not disintegrated at all, despite being exposed to the elements for over a year.

As stated, the day has no specific observances nowadays. Nevertheless, it bears a festive character, and is considered auspicious for marriage.