This article discusses the notion of the fluidity of sexual identity in light of Luce Irigaray’s account of sexual difference. I examine the historicity of sexual identity fluidity in relation to femininity as discussed in Irigaray’s second-wave feminism in order to show that the concept of sexual fluidity has to be configured by the concept of sexual difference if it wants to be productive, creative, and transformative. I will advance this claim with the help of Irigaray’s dual (reproductive and productive) notion of mimesis, which will allow me to distinguish between the ontology of sexual difference and the ontology of sexual fluidity. I will show that, from Irigaray’s perspective, the philosophical starting point to think sexual identity should not be sexual difference vs. fluidity but rather sexual dissymmetry vs. symmetry. On this account, one ought to acknowledge the historical, symbolic, and material reality of sexual difference.