Internationalization constitutes a broadly widespread concept in the literature about management. However, it has recently started being applied to higher education institutions. In this paper, we investigate internationalization in university institutions from both theoretical and empirical perspectives. To achieve our aim, we place particular emphasis on the methodology applied to evaluate the internationalization of higher education institutions from both quantitative and qualitative approaches. We focus on the study of the three most widely accepted higher education institution rankings: Times Higher Education Supplement, Academic Ranking of World Universities and Webometrics Ranking. We find that, while the variable internationalization is included in such rankings through several items, its weight in the overall score is still limited. Additionally, our results demonstrate that the final position achieved by university institutions is hardly determined by their degree of internationalization, but rather relies on other institutional aspects, such as teaching quality and research quality, among others. Furthermore, we argue that internationalization indicators used in current university institution rankings, e.g., international faculty ratio and international students ratio, are far from reflecting the main variables involved in their internationalization processes.