Rochdale, England, is known by millions for one reason: a handful of labourers established a co-operative there in 1844 known as the Rochdale Society of Equitable Pioneers. That co-operative was adopted as the inspiration and model for a movement that now includes nearly 700 million people around the world. As this paper is being written, co-operators around the world are preparing to celebrate the 150th anniversary of its birth. But what did Rochdale mean? Why is it considered so important?