During the past three hundred years, the conceptualization of sexual ignorance developed in dynamic opposition to changing knowledge systems and regimes of truth. As what there was to know about sex and reproduction changed, so did the meaning of knowledge and the significance of knowing. This chapter explores shifting understandings of sex and reproduction, alongside debates about the nature of sexual knowledge and who had, or should have, access to it. It examines the politics of knowing and not knowing, and practices of communication. It considers the reading and translation practices through which knowledge was shared, rumoured, sold, displayed or censored, and the mechanisms through which different forms of knowledge were grounded as reliable or truthful. It argues that sexual choices and bodily experiences were profoundly shaped by the changing structural dynamics through which sexual knowledge and sexual ignorance were opposed, produced and socially maintained.