The town of Mondragón in the Basque Country is home to one of the largest and most significant experiences of co-operative organization and workers’ self-management anywhere in the world. The Mondragón co-operative movement, born in the 1950s around the local technical training college and a handful of small industrial firms, encompasses today more than one hundred co-operative firms operating in ninety-seven countries and generating an aggregate revenue of €12bn. In this chapter we review the historical origins of the Mondragón experience and the goals that guided the first co-operative projects. After describing the key organizational principles and governance mechanisms of individual co-operatives and of the Mondragón group as a whole, we will examine the rapid expansion and internationalization of some of the most emblematic Mondragón firms—a process that has led to a difficult balance between the maintenance of the original co-operative principles at home and an increasing reliance on capitalist forms of ownership and production abroad. We conclude by discussing the impact of the recent economic downturn on the Mondragón group and its system of inter-co-operative solidarity, and by reflecting on the future prospects for this far-reaching experiment in collective ownership and democratic governance.