Many European countries have been introducing different measures to improve gender diversity at companies' top levels. using a sample of Italian, English and German listed companies, we present which impact different approaches toward gender diversity in boards of directors have on companies' performance. In 2011 Italy introduced mandatory gender quotas. Only in 2015, Germany followed this example. In United Kingdom, non-mandatory recommendations were announced in 2011. Comparing firms before and after the reform, we demonstrate that quotas are linked with a greater share of women. We then assess whether the share of women instrumented by the reform has an influence on our performance measures. We are able to state that quotas are a valid instrument to predict the share of women in the board and we find a significant and positive impact on firms' results when considering both profit margin and ROE as measures of performance. In order to have more robust results, we also use a difference-in-difference estimation and a semiparametric analysis. Not only our results let us exclude the existence of a negative correlation between the presence of women in boards and companies' performance, but we can also say that the increase of the share of women in boards leads to improved firms' outcomes for certain performance measures. Therefore, our results are consistent with gender quotas leading to a beneficial effect for companies.