With reference to theory and research, this chapter discusses the hidden curriculum of language textbooks and other teaching materials where culture, gender, race, or other topics associated with equality, diversity, and representativeness were presented in biased ways. Hidden curriculum may describe, present, or elicit stereotypes and reproduce cultural, gender, and racial bias in subtle ways; sometimes even teachers may not notice what the curriculum refers to or they may perceive stereotyping as harmless. This makes sociolinguistic problems with regard to use of a purist and monolithic cultural content more salient than ever. Yet, the new sociolinguistic landscape of language teaching where changing needs of language learners might not be accurately represented in teaching materials require the revision of current curricula and pedagogical practices. Therefore, this chapter draws conclusions from empirical studies on the topic and provides some implications for teaching and materials design