The article aims to show the key determinants of the development of early internationalizing companies (EICs). The early and quick internationalization of companies is an increasingly common trend that has been the subject of numerous research projects in many countries. It is an important area of studies focusing on the mechanisms of companies’ internationalization. The author critically analyzes some of the most significant international scientific papers of the last few years, with a special focus on the external and internal determinants of internationalization of EICs, the industries where EICs operate (both hi-tech and traditional) as well as these companies’ strategies in the area of foreign market entry and marketing. The typical characteristics of EICs are compared in the article with those of traditionally internationalized firms. The success factors of EICs in international markets have also been identified on the basis of research in this area. Finally, major threats to the development of EICs and the strengths of these firms are presented.