Using a unique database of over 20 million firms over two decades, we examine the industry sector and national institution drivers of the prevalence of women directors on supervisory and management boards in both public and private firms across 41 advanced and emerging European economies. We demonstrate that gender board diversity has generally increased, yet women remain rare in both boards of firms in Europe: approximately 70% have no women directors on their supervisory boards, and 60% have no women directors on management boards. We leverage institutional and resource dependency theoretical frameworks to demonstrate that few systematic factors are associated with greater gender diversity for both supervisory and management boards among both private and public firms: the same factor may exhibit a positive correlation to a management board, and a negative correlation to a supervisory board, or vice versa. We interpret these findings as evidence that country-level gender equality and cultural institutions exhibit differentiated correlations with the presence of women directors in management and supervisory boards. We also find little evidence that sector-level competition and innovativeness are systematically associated with the presence of women on either board in either group of firms.