<p>Horizontal gender segregation persists and is higher in more developed countries (gender-equality paradox). According to the theory of gender essentialism, more developed countries are characterized by more individualism, which in turn pushes individuals to rely more on personal characteristics when deciding about their future careers. The presence of both essentialist beliefs on gender and the endorsement of the stereotypical beliefs that math and science are “for boys” could explain the so-called paradox. By exploiting the large dataset collected by Project Implicit, the study tested the different associations of gender essentialism and implicit and explicit gender stereotypes with attitudes toward science of young women aged 15–19 in 51 countries. The results confirmed that both essentialist and stereotypical beliefs are negatively associated with attitudes toward science, still with differences in the strength of the association. Furthermore, the association between gender essentialism and attitudes toward science is stronger in more developed countries.</p>