This article articulates a conceptual foundation for co-operative behaviour. This foundation – known as ‘co‑operativism’ – consists of a social philosophy, economic principles, and psychology. For co-operativism to be a specific and realistic programme, it must take account of obstacles to co-operative behaviour and overcome them. This article derives co-operativism from a critique of capitalist economics, social philosophy, and psychology which impede co-operative behaviour. Co-operativism thus has a political dimension that strives for material, social, ideological, and psychological change. The logic of co-operativism is articulated through a series of examples from less collectivised praxis and self-concept to more collectivised. The increased economic, social, and psychological benefits of the ascending levels are explained. The article uses the different levels of co-operativism as criteria for analysing co-operative practices in the United States. Shortcomings in co-operative practices can be ameliorated by striving for the highest level of co‑operativism. The article is an activist programme for guiding organisations to promote high levels of co‑operative behaviour; it is also a treatise on co-operativism that contributes to the social sciences, economics, philosophy, social policy, and conflict resolution. The article informs activism with a scholarly basis, and it informs scholarship about co-operative behaviour with practical examples and consequences.