The curriculum shapes much of the school day. Students spend 80% to 95% of classroom time with curricular materials, including textbooks, and teachers make a majority of their instructional decisions based on these materials. These materials are far from objective and biases emerge. Gender bias, for example, teaches many harmful, if unintended lessons. Studies on curriculum from around the world indicate that females are underrepresented and that both males and females are depicted in gender-stereotyped ways. This entry reviews the research on gender bias in the K–12 school curriculum in the United States, explores seven forms of curricular bias, and discusses how gender bias influences what students learn in school.