During some of the days of the period of the counting of the omer, several mourning customs are practiced: Weddings are not held and one may not have a haircut. According to some, one should try to avoid reciting the Sheheheyanu blessing, which is normally said when buying significant new items of clothing or major household goods, or when tasting a fruit for the first time in its season. Some are strict about not listening to instrumental music. The reason for this observance of mourning is that according to a tradition of the Sages, 24,000 students of Rabbi Akiva (who was from the third generation of the tannaitic period and one of the greatest and most influential scholars of that period) died in a plague during these days, because they did not treat one another with respect.

The period during which Rabbi Akiva’s students died was thirty-three or thirty-four days. Accordingly, some observe the customs of mourning only until Lag BaOmer, the thirty-third day of the omer counting, which, according to one tradition, was the day that the students of Rabbi Akiva stopped dying. Ashkenazim are lenient with regard to the observance of mourning on Lag BaOmer itself (the eighteenth of Iyar), whereas Sephardim continue with some of the mourning practices until the following day, the thirty-fourth of the omer (the nineteenth of Iyar).

In contrast, some begin the mourning period only from the first of Iyar, because Nisan is a month during which mourning should not be observed. They then continue until the day before the festival of Shavuot, with the exception of Lag BaOmer, on which, according to all opinions, no students died. Here too, the number of days of mourning amounts to thirty-three.

Some observe the customs of mourning throughout the period of the counting of the omer, except for the days of Passover, Rosh Hodesh Iyar, Rosh Hodesh Sivan, Shabbatot, and Lag BaOmer, which together add up to sixteen days. Taking into account these days of exception, the days of mourning are once again thirty-three.

In light of the different customs, it is appropriate for each person to ask his rabbi how to conduct himself regarding the omer and its observances. This is particularly relevant in determining possible wedding dates during the period of the omer.