Sexuality constitutes an important aspect of sustainable development as the concept is used by the United Nations. Education is commonly viewed as crucial to achieving sustainability, and promoting action competence is a key element in such educational efforts. This suggests that education should support individuals in actively seeking information and acting in relation to sustainability challenges. This article aims to understand the role of textbooks in promoting action competence for sustainable sexuality by analysing content about sexuality in Swedish lower secondary school textbooks in biology and religious education. Results show that sustainable development and sexuality are organised as separate topics in all the books. Textbooks in biology contain a fair amount of sexuality education content, but content in religious education textbooks is more limited. In general, sexuality is closely linked to reproduction and is marked by androcentrism, phallocentrism and ideals of monogamy. Content about sexuality is furthermore strongly normative and seldom introduces readers to different theoretical perspectives or viewpoints. Taken together, these factors limit the extent to which existing textbooks can promote action competence for sustainable sexuality.