The seventeenth of Tamuz is a fast day. The main reason for the fast is that on that date, the walls of Jerusalem were breached by the Romans, a significant step in the process of the destruction of the Temple. Several other dramatic events also occurred on that date that left their mark on Jewish history: Moses broke the tablets of the Ten Commandments when he descended from Mount Sinai and found the Israelites worshipping the Golden Calf. The daily offering, which was sacrificed in the Temple twice each day, in the morning and in the afternoon, was forced to come to a halt. Furthermore, on the seventeenth of Tamuz, a Roman general named Apostomus publicly burned a Torah scroll. In addition, an idol was placed inside the Temple.

Further reading: For more on the breaking of the tablets, see A Concise Guide to the Torah, p. 218; A Concise Guide to the Sages, p. 120.

In general, the laws and customs of the day are similar to those of the fast of Gedaliah (see p. 156). The fast of the seventeenth of Tamuz begins at dawn (about an hour and a half before sunrise) and ends at the emergence of the stars. The precise times can be found in synagogue calendars.

The fast includes only a prohibition against eating and drinking, and it applies to every male over the age of thirteen and female over the age of twelve. Pregnant and nursing women need not observe this fast. In a case of illness, weakness, or any other difficulty in fasting, one should consult a rabbi.

There are several additions to the prayers of the day:

In the morning service, the prayer leader inserts the prayer Aneinu (“Answer us, God, answer us, on the day of our fast”) in the Amida, after the seventh blessing, the blessing of redemption. At the end of the prayer leader’s repetition of the Amida, the congregation recites Selihot. Next, the ark is opened for the Avinu Malkeinu prayer, followed by Tahanun. Then a Torah scroll is taken out of the ark and read. The reading is from Exodus (32:11–14; 34:1–10), and discusses Moses’ request from God to have mercy on the children of Israel and forgive them for their sins.

In the afternoon prayer service, after Ashrei (Psalms 145), the same Torah passage that was read in the morning is repeated, but in the afternoon a haftara is read as well, in Ashkenazic congregations. This haftara (Isaiah 55:6–56:8), which opens with the words: “Seek the Lord when He is found,” deals with leaving behind one’s sins and drawing closer to God. In the Amida, in the blessing of Shome’a Tefilla (acceptance of prayer), each individual adds the aforementioned Aneinu passage. As with the morning prayer, the prayer leader inserts the prayer Aneinu in the Amida, after the seventh blessing. In Israel, it is customary for the priests to recite the priestly benediction (Numbers 6:24–26) if the prayer is taking place toward the end of the day. After the Amida, the congregation adds the Avinu Malkeinu prayer, which is recited with the ark open, followed by Tahanun.

When the seventeenth of Tamuz falls on a Shabbat, the fast is postponed to Sunday, the eighteenth of Tamuz, and all the laws of the day mentioned above apply.