Partners in intimate relationships, because they have each other to rely on, have generally been considered safe from the negative consequences of social isolation. Here, we question this assumption, suggesting instead that social isolation may pose a threat to couples by depriving them of the tangible and emotional support that couples are likely to need, especially when confronted by stress. After briefly reviewing theoretical frameworks relevant to this idea, this article summarizes existing research documenting (1) associations between network ties and relationship outcomes, (2) mediators of these associations, for example, support and approval, and (3) moderators of these associations, for example, relationship qualities and cultural differences. We conclude by describing a research agenda to address methodological limitations in existing research and the policy implications of this line of work.