Leading up to Tisha B'Av (9th Av).
The Three Weeks is an annual mourning period that is shortly approaching. This is when we mourn the destruction of the Holy Temple and our launch into a still-ongoing exile.
The period begins on 17 Tamuz, a fast day that marks the day when the walls of Jerusalem were breached by the Romans in 69 CE.
It reaches its climax and concludes with the fast of the 9th of Av, the date when both Holy Temples were set aflame. This is the saddest day of the Jewish calendar, and it is also the date that many other tragedies befell our people.