Rapid changes in the external environment, the growing processes of globalization, increased competition, uncertainty and contingency in managerial decision-making are the characteristics of the current stage in the development of the economy. In such conditions, the network structures rather than firms become real production units. Combining the positive effects of cooperation inherent in hierarchical forms of organization and the preservation of incentives for market mechanisms based on property rights and the principles of competition provides the effectiveness of such network structures. The realization of the advantages of this organizational form demands from the participants the continuous improvement and management of enhancing cooperation. The article presents the stages of the development of interfirm cooperation, analyzes the evaluation methods, integrates the effects of network interfirm interaction into a single system as well as develops a multi-stage model for assessing the development of interfirm cooperation.