Farmers’ problems and co-ordination of agricultural activities cannot be solved simply by EU and/or government support, or by private market co-ordination institutions. Emerging producer groups and co-operatives seem vital in achieving bargaining power. Theoretically, and according to Western European (Dutch, Danish etc.) and US practical experience, one of the major important private institutions that can strengthen producers and help co-ordinate (agricultural) chains is the co-operative entity. To fulfill the basic co-operative aims and to compete in a more market-oriented environment (e.g. more liberal agricultural policies, opening European and world market, etc.) they will initiate new marketing strategies. To implement such new marketing strategies, co-ops have to collect more risk capital and in Western European agricultural co-operatives this is currently precipitating some fundamental financial and organisational changes. To retain the basic co-operative character, they are undertaking internal and external organisational changes, which in a number of cases will create so-called new co-operative structures/models. In this paper the “co-operative identity” concept (meaning the aims and functions of co-operatives, as well as the so-termed co-operative principles) is proposed to serve as a general theoretical background to evaluate economically the flexibility of (agricultural) cooperation. Also proposed is a new, interdisciplinary research focus (including comprehensive theoretical overview). This new focus examines the substance of co-operation and emphasises the importance of combining insights across the social sciences. It uses the results and common findings of economics, law, marketing, financing, organisational studies, management sciences (“hard” sciences), and also some elements of philosophy, psychology, sociology etc. (“soft” disciplines). Also recommended are some suggestions for further comparative research on the “co-operative identity”. This is carried out according to each country and different branches and sectors to observe the substance and dynamics of co-operation from different economic and non-economic aspects.