The study uses the two-stage bias-corrected DEA approach of Simar and Wilson (2007) to assess the efficiency of the EU countries in terms of their wind power investment in 2015. The set of input variables includes installed wind power capacity and average wind power density, while output variables include wind-generated electricity and three additional aspects: environmental, economic and energy security. Next, the study examines the effect of renewable energy policy regarding wind energy, the energy mix, and the offshore wind power utilisation on the wind power efficiency of the analysed countries. The results obtained reveal that the United Kingdom, Sweden, Denmark, and Ireland are the most efficient countries in terms of wind power investment. The inclusion of additional aspects demonstrates the greatest improvement of efficiency in Belgium, Cyprus, the Netherlands, Estonia and Germany. The results seem to indicate that economic instruments used within renewable energy policy have a positive effect on wind power efficiency, while policy support and regulatory instruments might negatively impact. Moreover, the results show that the energy mix explains the variation of the efficiency of the EU countries when their economic and environmental aspects are considered. The analysis of the geographic location indicates that countries with a high share of offshore wind capacity are the most efficient.