万圣夜（英语：Halloween，为“All Hallows' Eve”的缩写，意为“万圣节（诸圣节）的前夜”），意为万圣节前夕，中文常讹称为万圣节，在每年的10月31日，是西方世界的传统节日，主要流行于撒克逊人后裔云集的美国、不列颠群岛、澳大利亚、加拿大和新西兰等西方国家。当晚小孩会穿上化妆服，戴上面具，挨家挨户收集糖果。

万圣夜是诸圣节（All Hallows' Day）的前夜。其英语名称中的“Hallow”源于中古英语的“halwen”，与“holy”词源很接近，在苏格兰和加拿大的某些区域，诸圣节仍然被称为“Allhallowmas”，意思是在纪念所有圣人（All Hallows）的那一天要举行的弥撒（Mass）。

Trick-or-treating is a Halloween custom for children in many countries. Children in costumes travel from house to house asking for treats such as candy (or, in some cultures, money) with the phrase "Trick or treat". The "trick" is a (usually idle) threat to perform mischief on the homeowners or their property if no treat is given to them. It typically happens during the evening of October 31. Some homeowners signal that they are willing to hand out treats, for example by putting up Halloween decorations outside their door. Others might simply leave treats on their porch.