Hilchos Sefiras Ha’omer – 12

1. The custom is to not have one’s hair cut during the period of Sefiras Ha’omer. According to the Shulcham Aruchone may not take a haircut until the morning of the 34th day of the Omer, while according to the Rema it is permissible from the morning of Lag Ba’omer (the 33rd day of the Omer) itself (Shulchan Aruch and Mishnah 493).

2. According to the Kabbalists one should not have a haircut until the day of Shavuos eve (Kaf HaChaim ibid.).