The study focuses on issues of cooperation and reciprocity in the theoretical context, designated as mutualist approach. This approach is confronted with altruistic models of cooperation. The study is based on author ś long-term field research of cooperation during field works by farmers in Serbia. On the basis of the description of the origin, the process and the end of costly forms of cooperation, he sought to describe the social and psychological factors that are important for stable cooperation. In this context, emphasis is placed on the evolved sense for fairness and sensitivity to moral reputation and its evaluative and communication aspects which disseminate and stabilise the social norms of cooperation. Also attention is paid to conflicts of interest that motivated farmers to misuse cooperation, and to an analysis of the ways of resolving potential disputes. The results of the study show the sensitivity of peasants to the proportionality of their contribution and the benefits obtained from cooperation, including expectations regarding proportionality between their rights and obligations. When these expectations were not met, their cooperation ended. Due to the threat of open conflicts, they preferred less costly, symbolic sanctions or their institutional coverage. The key to stable cooperation seems to be the sticking to mutual benefits and mutual respect for farmers’ interests. Moreover, the mutualistic approach can also be used to describe many cases of altruistic help, which, however, does not exclude sincere willingness and an effort to help without claiming any reward.