This paper aims to investigate the evolution of economic theories that explain firms’ internationalization and the development of foreign direct investments. Arguments are intended to show that theoretical approaches in this field are rooted in the period of classical theories of the international trade. Theoretic fundamentals regarding the internationalization of the firm comprise of the literature review, mentioning the main theoretical trends based of which present understanding on transnational companies is formulated. Conclusions show that as the complexity of larger companies’ activity increases, the need for a new theoretical development to explain the relationships among different economic actors appears. Also, the evolution of the economic theories shows that a single theory cannot explain by itself the complexity of the present and especially of the future economic environment.