In this chapter, I argue that we can make sense of moral norms against consensual, adult incest by appealing to the value of familial relationships and the potential for sex to damage them. Viewing sex as unconscionable between family members helps to enable the loving intimacy normally associated with family relationships. Therefore, there is good reason for incest, even when consensual and between adults, to remain taboo. That being said, I argue that there is insufficient legal justification for all consensual, adult incest to be criminalised. I examine four potential arguments in favor of consensual, adult incest being illegal, and conclude that none of them succeeds in justifying a total legal prohibition against it.