Shiva Asar B’Tammuz, שבעה עשר בתמוז) the Seventeenth Day of Tammuz - is one of the four Rabbinically instituted Jewish fast days - commemorating the breach of the walls of Jerusalem prior to the destruction of the second Temple. This fast day marks the beginning of the three week mourning period which ends on Tisha B’av.

The fast commences at the break of dawn and ends after sunset. For people who can not start the day without their cup of coffee and for those that breakfast is the most vital meal of the day, waking up prior to the crack of dawn is an option.

Special prayers are added to the morning (שחרית) and afternoon (מנחה) prayers, as well a particular Torah reading and Haftarah.

If this fast day falls on Shabbat it is postponed to Sunday, as it is not permitted to mourn on Shabbat.
 

Mazor Guide to Shiva-ah Asar b'Tamuz (17th Day of Tamuz) brings you much more about the holiday, its meaning and its traditions... See the links below.

• Shiva-ah Asar b'Tamuz - 17th Day of Tamuz General Information
• Fast Days Commemorating Destruction of Temple
• 17th Day of Tamuz - a Day of Calamities
• 17th Day of Tamuz - a Day of Joy?
• The Three Weeks of Mourning Commence