International Workers' Day, also known as Labour Day in some countries and often referred to as May Day, is a celebration of labourers and the working classes that is promoted by the international labour movement and occurs every year on 1 May, or the first Monday in May.

May Day is a European festival of ancient origins marking the beginning of summer, usually celebrated on 1 May, around halfway between the Northern Hemisphere's Spring equinox and June solstice. Festivities may also be held the night before, known as May Eve. Traditions often include gathering wildflowers and green branches, weaving floral garlands, crowning a May Queen, and setting up a Maypole, May Tree or May Bush, around which people dance and sing. Bonfires are also a major part of the festival in some regions. Regional varieties and related traditions include Walpurgis Night in central and northern Europe, the Gaelic festival Beltane, the Welsh festival Calan Mai, and May devotions to the Blessed Virgin Mary. It has also been associated with the ancient Roman festival Floralia.