The book is structured like a dictionary and as such presents 23 short contributions, each with a different topic and an author’s profile and disciplinary perspective. All letters aim to show how diverse, rich and old is the co-operative sector worldwide. All letters discuss explicitly or not the ability of the co-operative sector to contribute to growth and development. Taken together, the letters provide a multidisciplinary explanation of how co-operatives contribute to our life, how they have been doing so for a long time, and, through reinvention, might still do so for years to come. All letters position the role of co-operatives with reference to traditional firms but do so in a critical rather than a polemical or utopian way.