Thematic Integration, as it appears across the depth-psychology corpus, names the process by which disparate psychological, narrative, or neural elements are brought into a coherent, functional whole without sacrificing their individual differentiation. The concept radiates outward from Siegel’s interpersonal neurobiology, where it designates the linking of differentiated parts into a functional system — a ‘central organizing principle for how the human mind develops across the lifespan.’ In this framework, integration is not mere amalgamation but a dynamic balance between complexity and coherence, threatened by dissociation and pathological rigidity alike. Alexander’s treatment of psychosocial integration extends the concept into socio-cultural terrain, emphasizing belonging and relational embeddedness as prerequisites for selfhood. McGilchrist’s hemispheric model reframes thematic integration as the irreducible dialectic between left-hemisphere analysis and right-hemisphere re-synthesis: analytic differentiation must return to the whole or produce only ‘concepts — abstractions and conceptions, not art at all.’ Hillman, characteristically, resists systematic closure, preferring mythology’s interrelated, unsystematized family of themes as a model for psychological complexity. Together, these voices chart the key tension in the literature: whether integration resolves into a stable synthesis or remains an ongoing, never-fully-achieved movement toward coherence.