The mother-infant relation stands as one of the most generative and contested sites in depth-psychological thought, drawing theorists into fundamental disagreements about the nature of early psychic life, the origin of the self, and the conditions under which development either flourishes or founders. Klein’s contribution is foundational: she locates the infant’s first object-relations in the encounter with the breast, tracing how splitting, projection, introjection, persecutory anxiety, and the depressive position all crystallise in this primal dyad. Winnicott reframes the same territory by insisting that ‘the infant and maternal care belong to each other and cannot be disentangled,’ privileging the holding environment, ego-support, and the good-enough mother as preconditions for the infant’s very existence as a psychological subject. Bowlby, drawing on ethology and empirical observation, rejects libido theory in favour of biologically grounded attachment behaviour, mapping individual differences in maternal sensitivity onto secure and insecure attachment patterns. Schore integrates all three traditions with neuroscience, showing how affect-regulatory transactions between caregiver and infant literally shape the developing brain. The Jungian tradition—through Fordham, Neumann, and Samuels—debates whether the infant begins as separate or uroboric, and whether the mother functions as the carrier of the child’s self. Across this range, the mother-infant relation serves as the primary explanatory lever for adult psychopathology, therapeutic regression, and the origins of intersubjectivity.