The paper discusses some internationalization theories of the firm. The authors look for key factors behind internationalization processes, with a special emphasis on experience and knowledge as the determinants of the internationalization strategy of firms. The review begins with a presentation of the Uppsala model and the approaches to internationalization developed by Cavusgil; Bilkley and Tesar; Cieślik; and Korth. Then the authors highlight concepts perceiving internationalization as a kind of innovation in the strategy of the enterprise as well as the concept of simultaneous internationalization. At the end of the paper, the authors draw the reader’s attention to a network approach toward internationalization. The analysis made in the paper allows the authors to conclude that the key determinants of the firm’s internationalization process come from the competitive potential of the company as well as the firm’s environment. Some theories of the foreign expansion of enterprises focus on internal factors, while others stress external factors. It seems that the best method is an eclectic approach and taking advantage of the complementary character of the theories discussed, the authors say.