The International Workingmen's Association (IWA) or International Workers' Association (1864–1876), often called the First International, is an international organization that aims at uniting a variety of different left-wing socialist, communist and anarchist political groups and trade union organizations that are based on the working class and class struggle.

It is founded in 1864 in a workmen's meeting held in Saint Martin's Hall, London.

Its first congress is held in 1866 in Geneva.In Europe, a period of harsh reaction had followed the widespread Revolutions of 1848.

The next major phase of revolutionary activity begains almost twenty years later with the founding of the IWA in 1864.

At its peak, the IWA has 5 million members according to the police reports, although the official journal reportes 8 million members.