This paper examines the evolving pattern of gender diversity of the boards of directors of leading Norwegian and British companies on a longitudinal basis. The period covered by the study covers the run up to proposed affirmative action legislation in Norway and, as such, affords an insight into corporate actions in this emerging institutional context. The findings demonstrate that, while board diversity has grown substantially in both countries in recent years, it has done so considerably more rapidly in Norway than in the United Kingdom. The analysis highlights the sectoral variation between the countries in the pattern and growth of board diversity and suggests that the vast majority of the overall growth in board diversity is the result of changing firm behaviour rather than sectoral shift in the United Kingdom or Norwegian economies. It is also shown that as diversity has increased there has been no fall in how experienced female directors are; neither is there evidence of a rise in the number of boards that female directors sit on. This suggests that the rapid growth in board diversity has been achieved without any fall in the quality of female directors.