This study develops a typology of social networks of individuals with a borderline diagnosis. Additionally, it reconstructs how those affected perceive themselves in relation to their interaction partners and how this self-image evolves throughout their biographies. The results call for a critical reassessment of concepts that attribute an inability to maintain stable social relationships and an unclear self-image to physiological factors or once-acquired traits of individual personalities. Instead, following agency discourses, the dynamic interplay of identity and social relationships is conceptually appreciated. This leads to a changed understanding of borderline: less as a pathological trait of individuals, but rather as an interactive practice of identity work and maintenance.