Labor Day, also known as May Day, is observed worldwide on May 1, celebrating the achievements of workers and the labor movement. The holiday has its origins in pre-Christian spring festivals and evolved into a secular celebration after the Christianization of Europe. It was formally established in the late 19th century as International Workers' Day to commemorate the Haymarket riot in Chicago on May 4, 1886, and is actively promoted by various labor organizations, including communists, socialists, and anarchists. In many countries, May Day is a public holiday, while in others, such as the United Kingdom and Ireland, it is celebrated as a bank holiday on the first Monday in May. Activities typically include parades, demonstrations, and various festivities that honor workers' rights and contributions.