Even though gender quotas are increasingly adopted, the legitimacy of such measures remains an issue of controversy. In this contribution, we ask how MPs, i.e. the key players in the implementation and adoption of quotas, think about affirmative action, and under which conditions they find quotas to be legitimate measures for improving gender equality. Our results reveal that much variation exists as to how MPs perceive the legitimacy of quotas. This variation plays out at both the individual and the macro level. Women and left-wing MPs consider quotas to be more legitimate than men and right-wing MPs. The openness of the parliamentary arena towards women’s movement proves to be an important condition for the positive evaluation of quotas. The broader electoral and parliamentary context only has a conditional effect: it influences female MPs’ assessment of quotas but not that of male legislators.