In this article we explore two sex-related questions. First, what have the authors of utopias and dystopias said about sexual behavior and relationships in their works? In examining this question, we seek to identify different modes of sexual behavior or relationships that have been presented as characterizing the good or bad society. Second, what is the role of sex in utopia and dystopia? Is there a sexual element of how to get from here to there? Can changes in sexual behavior and relationships help bring about the good society? In order to explore these questions we consult a large number of primary sources, and our discussion begins with a broad-brush survey that establishes some early norms and variations from the canon of utopian thought. Two recurrent themes emerge from this survey: the first concerns a tripartite relationship among sex, sexuality, and gender. The second concerns sex and control. Both themes reinforce key modes of sexual behavior, which are explored in the final section of the article, where we undertake a deeper consideration of sample texts from three authors: Marge Piercy, Robert Rimmer, and Alex Comfort.