Gender mainstreaming was introduced within the European Union (EU) in the 1990s as a means of addressing the unequal treatment of employed women. Yet its impact on organizational practices in Europe has been limited. This review synthesizes and analyses theoretical and policy literatures on gender mainstreaming within the EU between 1998 and 2011. It highlights ambiguities within gender mainstreaming literatures regarding whether gender mainstreaming is, first and foremost, a policy or a strategy. It further identifies ambiguities regarding how inequality should be articulated: in terms of the sameness or difference between women's and men's concerns, and in the context of whether gender mainstreaming research should be defined as focusing primarily on ‘women’ or on ‘gender’. The paper suggests that such ambiguity of definition within gender mainstreaming literatures compromises the implementation of gender mainstreaming within organizational practices. It further observes the need, within some gender mainstreaming theoretical and policy literatures, to move away from stable definitions of ‘male’ and ‘female’ (which identify women's and men's concerns as often in contrast) towards a more situated approach. The paper contributes to future gender mainstreaming research by proposing a more fluid, post-structural and sociocultural interpretation of ‘gender’. Drawing upon Judith Butler's research, it argues for the reconceptualizing of gender mainstreaming through a ‘Gender as performativity’ framework, in which gender is characterized as situational and performed in line with organizational expectations about women's and men's social roles