This chapter introduces the interdisciplinary field of relationship science. It describes the human drive for belonging, including the biological underpinning of sociality and the harmful consequences of social isolation and social exclusion. It also defines romantic relationships and the characteristics that differentiate romantic relationships from other close relationships (high interdependence, high intimate knowledge, high commitment). In addition to emphasizing the core commonalities across romantic relationships, this chapter explores the many ways in which romantic relationships are diverse (e.g., structure, exclusivity, composition, duration, motives). Finally, this chapter highlights the critical importance of close relationships for individual health and well-being as well, as for society more broadly.

In addition to facilitating reproduction and gene propagation, partner attractiveness facilitates pair-bond maintenance. For this reason, partner attractiveness is a core issue for women’s long-term relationships. In this chapter, in addition to explicating the qualities that comprise partner attractiveness for women and their functions, we discuss the extent to which the functional importance of these qualities may shift situationally within the context of women’s committed, long-term relationships. Traits signaling (a) social status, access to resources, and willingness to share resources and (b) physical health and genetic benefits can confer direct benefits to offspring and thus women’s attraction to such traits can facilitate reproduction. Although research to date suggests women’s attraction to traits signaling social status, access to resources, and willingness to share resources does not shift over contexts or the life-course of women’s long-term relationships, women’s attraction to traits signaling physical health and genetic benefits seem to fluctuate across fertility status (though some mixed evidence has emerged). Moreover, the function of such traits may shift as women’s long-term relationships develop over time. We highlight each of these shifts in turn. Traits signaling commitment and trustworthiness (e.g., commitment, supportiveness, warmth, kindness) facilitate long-term relationship maintenance. Given relationship maintenance is consistently important to women, such partner qualities are a stable component of partner attractiveness; nevertheless, we raise the possibility that women’s attraction to such traits may heighten at key milestones in women’s relationship (e.g., during the transition to parenthood, when reaching older age). We end this chapter by proffering an evolutionary developmental relationship life-course model that (a) synthesizes the literature on shifts in partner attractiveness for women and their implications for women’s relationships, (b) suggests new ways of thinking about partner attractiveness, and (c) reveals gaps in empirical knowledge that can pave the way for future research.