In today's environment of deregulation, intensified competition, rapid technological innovation, consequent institutional change, and the coexistence of competition and cooperation, it is more important to understand the firm as an evolving entity embedded within institutions rather than to view it under neoclassical assumptions. From this perspective, the importance of new institutional economics—which includes institutions in its analytical scope and develops under more realistic assumptions—has been increasing. In particular, research on firm theory developed from the perspectives of transaction cost economics, property rights economics, agency theory, and evolutionary economics, as well as research on inter-firm relationships based on network theory, has been actively pursued. Since these domains overlap with the scope of business administration, the need for examination from an interdisciplinary research perspective can be raised for a more systematic understanding and explanation of firm behavior. In particular, the concepts of institutions, contracts, transaction costs, bounded rationality, opportunism, governance structures, trust, cooperation, and evolution proposed by these approaches are core concepts of both old and new institutional economics, and can be used to broadly explain the organization and behavior of firms in dynamic environments, suggesting that their implications for business administration will increase in the future. In this context, the main purpose of this paper is to coherently examine the firm and inter-firm networks as an extended form of the firm within a new institutional economics framework through a literature review, while also systematizing the macro-level relationship between institutions and firms, exploring the establishment of an integrated theory of the firm, and deriving the core element structure of the firm necessary for such a model.