EN
Measuring the degree of internalisation of a firm is important for many reasons. Internationalisation of a firm is perceived as being related with many aspects of its performance i.e. innovativeness, competitiveness or efficiency. The most popular complex internationalisation indexes are usually applied to assess the degree of internationalization of the most internationalised, large transnational corporations. There is a little use of these indexes in measuring the degree of internationalization of firms in their early stages of internationalisation, such as the Polish firms are. The aim of the paper it to review the contemporary theoretical approaches to internationalisation of firms and derive some methodological assumptions concerning its measurement. It should help in creating more complex internationalisation indexes which could be used in measuring the degree of internationalisation of such firms.