The Day of the Holy Innocents is observed on December 28.

This day recalls the biblical event known as the Massacre of the Innocents, where Herod, the king of Judaea, will have condemned all the boys in the village of Bethlehem to death, for fear of losing his throne to the newborn "King of the Jews", announced by the three wise men.

The murdered boys became known in the Church as the "Holy Innocents" and as the first Christian martyrs.

The first commemoration of the Day of the Holy Innocents in the western church dates back to the year 485, in the "Leonine Sacramentary". The date of the celebration of April Fools' Day varies between the 27th and the 29th, depending on the type of Church. For the Catholic Church, the Church of England and the Lutheran Church, the date of the celebration is December 28.