Wind energy has grown from less than 20 gigawatts (GW) in 2000 to 590 GW by the end of 2018 and already provides 6% of the electricity consumed in the world. During this period, the wind energy technology industry has evolved from a local to a global business. To illustrate the globalization of this sector, this research assesses the effectiveness of the firms' international strategies based on empirical indicators. The intensity, the speed of internationalization, the geographic extensity and diversification are calculated and analyzed. The results indicate that the most successful firms are the market leaders Vestas and Siemens Gamesa Renewable Energy, and they are characterized by leading in both the depth (sales abroad/total sales) and width (number of countries) of internationalization as well as in geographic diversification. These companies are closely followed by four European and American firms: Enercon, Nordex, General Electric and Senvion. To date, Chinese firms, leaders in the largest market (China), are in general unable to internationalize as effectively as firms from other constituencies. Our results reveal that strong rivalry pressure in the domestic market is not a guarantee for the international competitiveness of its best-performing firms in the case of the wind energy industry e unless there are special characteristics in that domestic market. (C) 2020 The Authors. Published by Elsevier Ltd.