What are sexual fantasies, and what roles do they play in relationships? Fantasies are sometimes (but not always!) a window into what people want to experience in their own relationships—what do fantasies tell us about relationships? Do they help us get closer to a monogamous partner, or do they drive us apart? Could they be a way to promote communication among partners? Do women and men fantasize differently? And if so how? These are some of the questions we will be addressing in this chapter. Specifically, in this chapter, we explore the role of sexual fantasies in romantic relationships and investigate the potential advantages and disadvantages of sexual fantasies within the context of romantic relationships. Additionally, we discuss women’s sexual fantasy preferences and look at findings that suggest that women, more so than men, indicate that submission is among their favorite or most frequent sexual fantasies (Arndt et al. in J Pers Soc Psychol 48:472–480, 1985; Crepault et al. in Prog Sexol 267–285, 1976; Davidson and Hoffman in J Sex Res 22:184–205, 1986; Hariton Psychol Today 1973, March; Hariton and Singer in J Consul Clin Psychol 42(3):313, 1974; Kanin in Victim Int J 7:114–121, 1982; Knafo and Jaffe in J Res Pers 18:451–467, 1984; Pelletier and Herold in J Sex Res 24(1):250–256, 1988; Talbot et al. 1980). Finally, in an attempt to better understand this gender difference, we present and investigate three potential explanations.