The 1st of May, or first Monday in May, is a national public holiday in many countries, in most cases known as "International Workers' Day" or a similar name.

The 1904 Sixth Conference of the Second International, called on "all Social Democratic Party organisations and trade unions of all countries to demonstrate energetically on the First of May for the legal establishment of the eight-hour day, for the class demands of the proletariat, and for universal peace".