The Birth of the Báb is a Bahá'í holiday commemorating the birth of the Báb (Sayyed `Alí Muḥammad Shírází) on October 20, 1819. Along with the Birth of Bahá'u'lláh, it is one of the "Twin Holy Festivals" or "Twin Birthdays" of the Bahá'í Faith.
The Twin Holy Festivals were observed on the first and second days of Muḥarram in the Islamic calendar until 2014, when the Universal House of Justice decided that they should be celebrated "on the first and the second day following the occurrence of the eighth new moon after Naw-Rúz." This means they may occur in different months each year (both on the Bahá'í calendar and Gregorian calendar), but will always occur together.