During the days of the Omer, the students of Rabbi Akiva died, over a period of thirty-three days. Therefore, we observe several mourning practices during part of the Omer. However, this does not apply to the entire period of the Omer, as will be explained below.
Sephardim: Those who follow the ruling of the Beit Yosef do not take haircuts or get married until the morning of the thirty-fourth day of the Omer. Similarly, during these days, listening to music, whether instrumental or on the radio, is prohibited.
The Ari”zal: His custom was not to have a haircut throughout the Omer until the day before Shavu’ot. According to this custom, even a groom on his wedding day should not take a haircut or shave during the Omer.
Ashkenazim in Israel who follow the Ari”zal: Their custom is allow marriage and haircuts on the thirty-third day of the Omer (Lag B’omer), and from Rosh Chodesh Sivan. However, before and on Rosh Chodesh Iyar, between Rosh Chodesh Iyar and Lag B’omer, and between Lag B’omer and Rosh Chodesh Sivan, they observe the customs of mourning. Most of them only take a haircut on the day of Lag B’omer, and not at night. Similarly, marriages are held on the day of Lag B’omer, and not at night. However, under pressing circumstances, they may take haircuts or get married on the night of Lag B’omer. Nowadays, many are lenient and get married on the night of Lag B’omer.
Some Ashkenazim have the custom to permit haircuts and marriages until Rosh Chodesh Iyar, and then prohibit them until Shavu’ot, except for on Lag B’omer. Some are stringent and prohibit them on both days of Rosh Chodesh Iyar, and permit them during the three days before Shavu’ot.
Marriage: The custom not to marry applies also to second marriages, including a widower who marries a widow. However, one may re-marry one’s ex-wife, even before Lag B’omer.
Engagement: One may get engaged and make a festive engagement meal. However, musical instruments are not allowed and dancing should be kept to a minimum. According to the Mishnah B’rurah, dancing is prohibited.
Bar-mitzvah: One who becomes bar-mitzvah during the Omer is called up to the Torah, and one may make a meal in honor of the bar-mitzvah and sing. Musical instruments, however, are not allowed.
Songs: One should be careful not to listen to even holy songs, from a radio or other media until Lag B’omer.
Cutting hair: The Sephardim customarily do not cut hair until the morning of the thirty-fourth day of the Omer, because that was when the students of Rabbi Akiva stopped dying. One may have a haircut from then on, until Shavu’ot.
It is the custom of the Ari”zal not to take a haircut until the day before Shavu’ot. According to the Rema, one may take a haircut during the day of Lag B’omer, but not at night. The Mishnah B’rurah permits haircuts on the night of Lag B’omer.
If Lag B’omer is on a Friday, Ashkenazim cut their hair in honor of Shabbat.
If Lag B’omer falls on Motza’ei Shabbat, according to the Beit Yosef, one may not have a haircut on Friday. According to the Rema, it is permissible.
According to the Ari”zal, even though, one should not have a haircut until the day before Shavu’ot, if Shavu’ot falls on a Sunday, one should cut one’s hair on the previous Friday.
Brit Milah (Circumcision): The sandak, mohel and the father of the baby may take haircuts and shave on the day of the Brit Milah and even on the day preceding from the late afternoon onwards. However, the custom of the Ari”zal is to not cut one’s hair at all.
Cutting nails: It is permissible to cut one’s nails throughout the Omer.
Shehecheyanu: Some have the custom not to recite Shehecheyanu on clothes or fruit. Others recite on fruit but not clothes. According to both customs, one may buy new clothes during the Omer and wear them afterwards. However, the accepted custom is to recite Shehecheyanu on both clothes and fruit.
Melacha (work): It is customary for women not to do melacha from sunset until after counting the Omer, because that was the time of day that the students of Rabbi Akiva passed away. This is hinted at in the verseשבע שבתות , , from the root שבות, which means “abstain,” teaching us that one should abstain from work from sunset until one counts the Omer. (There are additional reasons for this.) Some have the custom to abstain from work all night. According to the Ben Ish Chai, it is proper for men to be careful about this too. However, this is only until Lag B’omer.