Over the last decades, agricultural co-operatives grew substantially in most developed and developing countries, often reaching dominant market positions. We inquire into the economic mechanism behind this growth, by elaborating on the relation between co-operative identity and co-operative benefits. We highlight the ability of agricultural co-operatives to co-ordinate large-scale production, to monitor work contributions and product quality, and to ensure economic independence of farmer members. Following the two principal streams in the economic literature, we distinguish between the conceptions of agricultural co-operatives as units of vertical integration and as firms characterized by common governance of collective entrepreneurial action and ability to reduce transaction costs and economic risk. We describe the financial and governance limitations of agricultural co-operatives while taking account of new co-operative models presenting institutional tools introduced to overcome these limitations. We conclude by suggesting directions for enhancing the role of co-operatives in agricultural and rural development.