Karl Marx is often thought of as primarily a theorist or philosopher, but as Marx himself famously stated, 'philosophers have only interpreted the world, the point is to change it'. This talk will discuss one of the main activist projects that Marx was centrally involved in, the International Workingmen's Association. This was the first truly international association of working class organisations, uniting workers around the world in the fight against capitalism. While involved in the IWA Marx dedicated almost all of his time to organisation and agitation in the workers movement, agitated for revolutionary socialist politics against both reformists and anarchists, and laid crucial foundations for radical working class parties to emerge all around the world.