New Institutionalism has shown that the ‘rules of the game’ are crucial to structuring political life in terms of constraining and enabling political actors and influencing political outcomes. A limitation of this approach, however, has been its overemphasis on formal rules, with much less attention paid to how informal rules work alongside and in conjunction with formal institutions to shape actors and outcomes. This article contributes to an emerging literature that highlights the importance of informal institutions by bringing into focus one element that has been hidden in these debates – the influence of gender norms and practices on the operation and interaction between formal and informal institutions. It highlights some of the key benefits of a gender analysis for understanding political institutions in both their formal and informal guise and considers some of the challenges in building a research agenda that requires new methods and techniques of inquiry.