The majority of previous research in the field of board diversity was dedicated to the direct link between board gender diversity and firm performance. Grounded in Agency- and Resource dependence theory, this thesis expands on this research and examines the main relationship including the influence of two additional factors: educational level of female directors and mandatory board gender quotas. Analyzing a sample of 454 European firms (3,871 firm-year observations) over the period 2007-2017, a positive relationship between board gender diversity and firm performance is found. Furthermore, the results suggest that educational levels or board gender quotas do not affect this relationship. The effects on firm performance differ depending on whether legislative measures or voluntary initiatives are in place, i.e. in contrast to legislative quotas, voluntary initiatives enhance firm performance.