The coronavirus-19 (COVID-19) pandemic has profoundly altered people's daily lives and created multiple societal challenges. One important challenge of this unique stressor is maintaining well-functioning intimate relationships, which are inextricably tied to emotional and physical health. Yet research on romantic relationships shows that external stressors such as economic hardship, demanding jobs, and disasters can threaten the quality and stability of couples' relationships. Research within relationship science investigating how external stressors and existing vulnerabilities shape couple functioning can inform predictions about how the current pandemic will impact couples' relationships and which couples in which contexts may be most at risk for adverse relationship consequences. Drawing on theory and research from relationship science, the presented conceptual framework, adapted from the vulnerability-stress-adaptation model (Karney & Bradbury, 1995), suggests that facing COVID-19-related external stress is likely to increase harmful dyadic processes (e.g., hostility, withdrawal, less responsive support), which will undermine couples' relationship quality. These harmful effects are likely to be exacerbated by the broader preexisting context in which couples' relationships are situated (e.g., social class, minority status, age), and their individual vulnerabilities (e.g., attachment insecurity, depression). The framework presented identifies the essential factors that need to be addressed in order to mitigate the potential adverse effects of the current crisis on relationships, and offers key directions for future research. Public Significance Statement The current article draws on relationship science theory and research to illuminate the potential consequences of the COVID-19 pandemic for couples' relationships. How well couples adapt will depend not only on the extent to which they face more severe COVID-19-related stressors but also the broader context of their lives (e.g., income, minority status) and couples' individual vulnerabilities (e.g., depression, attachment insecurity). This time of crisis raises opportunities for policies, interventions and couples to promote adaptive relationship processes and enrich the quality of couples' relationships.