I describe in this chapter how romantic relationships are initiated, including the literature on online dating relationships and its implications for long-term relationships. I describe the literature on mate selection, which shows that men prefer physical attractiveness more than women, that women prefer earning potential more than men, and that these differences are qualified by methodological issues. In the end, there are far more similarities than differences in the features of a mate that heterosexual and LGBT persons find attractive, and similarity is one of those. I discuss how men and women conceptualize love and sexuality, again noting more similarities than differences. Men may be more romantic than women, and also more sexually permissive than women. Women engage in more strategies to maintain relationships than men. In terms of conflict, I discuss the demand/withdraw pattern and show that its link to gender is primarily in terms of desire for partner change. The highly controversial literature on jealousy is presented, concluding that all except heterosexual men are more concerned with emotional than sexual infidelity. The chapter concludes with a discussion of cohabiting relationships, its prevalence, different motives, and outcomes.