Christmas Eve, December 24, the day before Christmas Day, is treated to a greater or a lesser extent in most Christian societies as part of the Christmas festivities. Christmas Eve is the traditional day to set up the Christmas tree, but as the holiday season has been extended several weeks back (to around Thanksgiving in the United States), many trees will have been set up for weeks.

Many Christians traditionally celebrate a midnight mass at midnight on Christmas Eve, which is held in churches throughout the world, marking the beginning of Christmas Day. Other churches like the Anglican Church hold Candlelight service which is typically held earlier in the evening. These often feature dramatizations of the Nativity. Large meals are common, often with turkey or ham as the main item. A traditional dish in Germany is roast carp.

It is also seen as the night when Santa Claus or his international variants, make their rounds giving gifts to good children. In Italy presents are opened on the morning of Christmas Eve, while in the United Kingdom, Ireland, Sweden, Denmark, Norway, Finland, Portugal and Poland, Christmas presents are opened on that evening or on the morning of Christmas Day. In North America, there is a mixture of families opening gifts in the evening and, more commonly, on Christmas Day morning. In families where a divorce has occurred, children may spend one day with one part of the family, and the next with the other. In Spain gifts are opened on the morning of January 6th, Epiphany day ("Día de reyes").