Non-suicidal self-injury (NSSI) is the direct, purposeful self-infliction of injury, which results in tissue damage, is performed without conscious suicidal intent and through methods that are not socially sanctioned (Nixon & Heath, 2009). The phenomenon of self-injurious behaviours is alarming, especially among adolescents and young adults (Muehlenkamp, 2005). In fact, it is estimated that lifetime prevalence of NSSI in young adults within the general population is around 12% to 38% (for reviews, see Heath, Schaub, Holly, & Nixon, 2009; Jacobson & Gould, 2007; Rodham & Hawton, 2009). While this proportion declines when assessing recent NSSI (i.e., usually performed in the past six months or in the past year), the numbers are still disturbing with 2.5% to 12.5% of young adults reporting current NSSI (for reviews, see Heath et al., 2009; Jacobson & Gould, 2007; Rodham & Hawton, 2009). The goal of this thesis is to investigate the associations between romantic relationships and NSSI in young adults and to address two major limitations that emerge from the literature, namely: a) several theoretical hypotheses have yet to be validated despite considerable advances in the scientific study of NSSI; and b) with the exception of one study, the few studies available relating romantic relationships and NSSI solely focused on the individual level of analysis instead of including both partners in the model. This goal will be addressed through three articles, each targeting specific objectives. For the sake of methodological rigor and for adequate evaluation of the constructs under study, the purpose of the first study was to validate the factorial structure of the English version of the Dyadic Coping Inventory (DCI; Bodenmann, 2008). A confirmatory factor analysis (CFA) corroborated the measurement theory of the DCI by revealing the presence of five coping factors (i.e., stress communication, supportive dyadic coping, delegated dyadic coping, negative dyadic coping, common dyadic coping) and two target factors (i.e., one’s own dyadic coping and partner’s dyadic coping). The English DCI also demonstrated good internal reliability and yielded preliminary evidence of concurrent validity. All together, these findings lead to the conclusion that the English DCI is an accurate and reliable measure of dyadic coping, and that researchers can use the English DCI confidently in their research to evaluate dyadic coping processes. The established factorial structure of the English DCI was then used in subsequent studies of this thesis. The purpose of the second study was to investigate direct and indirect associations between insecure romantic attachment, difficulties in emotion regulation and common dyadic coping strategies, and endorsement of NSSI behaviours. From an empirical standpoint, this study is the first to explore these specific relationships in one comprehensive model, targeting both interpersonal and intrapersonal strategies to deal with stressful experiences and the role it might have on one’s NSSI behaviours. Overall, the results revealed that difficulties in emotion regulation mediated the relationships between romantic attachment insecurity (i.e., attachment anxiety and attachment avoidance) and NSSI, whereas no such effects were found for common dyadic coping strategies. Findings from this study suggest that intrapersonal strategies (i.e., emotion regulation) might be more influential on one’s NSSI behaviours than behavioural strategies (i.e., common dyadic coping). This study also offers a first step towards the understanding of the romantic relational context of individuals struggling with NSSI behaviours. The next step remains to explore the couple as the unit of analysis rather than focusing on only one member of the relationship, giving way to the third study of this thesis. The primary aim of the third study was to generate a general portrait of young women’s romantic relationship functioning, distinguishing women who recently self-injured from those who have never self-injured. This study was designed to permit the exploration of not only the individual-level effects, but also potential effects from the romantic partner. Through a series of nonparametric Mann-Whitney U tests, results revealed that women who engage in NSSI behaviours are more likely to report subjective distress in the form of attachment anxiety and distrust compared to women who do not engage in NSSI behaviours. They also reported good, but slightly lower levels of, relationship satisfaction and adaptive dyadic coping strategies compared to women who have never engaged in NSSI. Findings also showed that partners of women who engage in NSSI behaviour reported more attachment anxiety than partners of women who do not engage in NSSI behaviours. The women and their partner’s reports about their romantic relationship experiences provide unique insight into the similarities and differences of individuals who self-injure and those who do not. Furthermore, a cursory exploration of the partners’ NSSI behaviours revealed that nearly one-third of the partners in a relationship with women who self-injured also reported having recently engaged in NSSI behaviours. These findings add some depth to the understanding of the relational context of those who are struggling with NSSI and provide future directions in research.