The paper analyzes approaches to interpretation of a competitive advantage source in various schools of strategic management. Systematizing concepts and approaches of foreign and national researchers within the framework of this or that strategy school the author of the paper gives preference to the Lakatos concept that various scientific-research programs may coexist and compete simultaneously. Strategic management science does not have any obstacle to compare competing theories in justifying sources of strategic competitive advantage. An internal logic of a theory serves as the basis to compare quality of verbal or formal school models, and consideration of successful / unsuccessful strategies in modern dynamically developing economy makes it possible to obtain data for empirical verification of the models. Purpose of the paper is to evaluate prospects of scientific-research programs proposed by various strategy schools in the context of their approaches to sources of competitive advantage. Evolution of science and practice in strategiс has led to shift in emphasis for understanding a company not as a set of business units but as a set of resources and competencies that contributed to obtaining a dominant position in strategic management of resource-based strategy concept. Search for sources of competitive advantage has been shifted to specific resources which a company possess. Such approach lays a solid foundation for a qualitative analysis of strong and weak points of the organization while forming a sustainable long-term advantage based on the development and protection of company's internal resources. Research of competitive advantage resources from the perspective of the concept of company’s dynamic abilities (modern stage of resource-based concept development) is considered as the most promising one because it is based on endogenous nature of advantage sources. This approach rejects implausible assumptions and emphasizes importance of an entrepreneurial factor.