Insecure attachment occupies a central and contested position across the depth-psychology corpus, functioning simultaneously as a developmental diagnosis, a phenomenological category, and a clinical explanatory framework. The literature traces its origins to Ainsworth’s Strange Situation research, which identified insecure-avoidant and insecure-ambivalent patterns as organized, if compromised, adaptations to caregiving failures — with Main and Solomon’s later disorganized category marking the outer boundary of relational dysregulation. Bowlby’s own theorization recast insecure attachment not merely as a symptom-producing deficit but as the generative source of secondary, pathological defenses — hyperactivating or deactivating strategies deployed in the face of unavailable or rejecting figures. Schore, Ogden, and Siegel extend this into somatic and neurobiological registers, demonstrating how insecure attachment patterns become encoded in body posture, arousal regulation, and cortical architecture. Flores and Winhall draw the attachment-addiction nexus, arguing that insecure attachment motivates the substitution of substances for unavailable relational objects. A further tension runs through the corpus between determinism and plasticity: Main’s work on ‘earned security,’ cited by Siegel, establishes that insecure histories need not foreclose secure functioning, provided transformative relational experiences intervene. The intergenerational transmission of insecure attachment — mediated, as Lanius documents, by deficits in parental mentalizing — gives the concept its most sobering clinical weight.