The paper discusses the mechanisms involved in the establishment of cooperative institutions and their roles. These institutions are based on a pact of indivisibility, agreements regarding resources and employment - and their use, according to coherent distributive rules - in a long-term perspective. Such a pact allows for the establishment of a common-by-contract, corresponding to the creation of a «process fund» needed for the integration of the production processes, the division of the labour and the specialisation of the labour force. Several commontypes are defined, as separate forms of co-operative enterprises. Particularly, these different forms display their competitive advantages on high contestable markets (agriculture, building, transports, services, etc.). The cooperative commons are the establishment of «public goods» on the filierewhich on the one hand, allow for economies of scale (and scope) and on the other hand, cut down transaction costs. The enterprise classification proposal, connected to the different types of commons, gives visibility to the different functional roles of the cooperatives. The empirical work is based on original data related to the 1948-2000 period.