How well are women represented in the world of political advocacy? Despite the important role of interest groups in modern democracies, the demographic composition of the interest group community remains a blind spot in public policy research. Based on data on over 1000 lobbyists in five European countries, we suggest that the share of women in the world of advocacy is significantly lower than in parliaments. We therefore argue that gender biases in political advocacy need to move high up on the research agenda. As key avenues for future studies, we raise the effects these imbalances have on agenda setting and political decision-making, as well as their symbolic effects on female participation and perceived legitimacy. Moreover, we call for research addressing the complex supply and demand-side factors that cause gender inequalities in lobbying to address this problem in practice.