The three weeks which begin on Shiva Asar BeTamuz (the seventeenth of Tamuz) and end on Tisha BeAv (the ninth of Av) are a period of mourning for the Jewish people. It was during this time that both of our Holy Temples were destroyed.
There are two periods within these three weeks. During the period beginning from Shiva Asar BeTamuz till the end of Tamuz (a period of twelve days) the mourning is not as intense.
The final nine days beginning with the first of Av till Tisha BeAv are much more intense. During these final nine days the mourning from the first twelve days is intensified and many additional practices of mourning are added.
During the first twelve days the following practices are observed:
During the final nine days we continue to follow these restrictions in addition to which we add the following practices:
In addition, it is preferable to not engage in disputes with non-Jews during the month of Av.