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 May Day.

In 1884 the American Federation of Organised Trades and Labor Unions demanded an eight-hour workday, to come into effect as of May 1st 1886. This resulted in the general strike and the Haymarket (in Chicago) Riot of 1886, but eventually also in the official sanction of the eight-hour workday. Three years later, a French socialist party created an international day to honour the labour movement and marked May 1 in commemoration of the Haymarket Massacre.