The concept of internalization is traced through two lines of theorizi
ng that include Freudian and social-learning accounts of socialization
and the sociogenetic theories of general mental functions and develop
ment held by Janet, Baldwin, and Vygotsky. An account of internalizati
on as transformation is presented. An analysis of earlier theorists' v
iews is proposed as a foundation for regarding internalization as a pr
ocess involving transformations of semiotic material imported from the
social world into personally constructed subjective experience. It is
argued that researchers who work within the increasingly popular soci
ogenetic tradition would benefit from making explicit the historical c
onnections between their versions of the concept of internalization an
d the thinking of major figures in sociogenetic theorizing. Explicit a
nalysis of internalization as constructive transformation makes it pos
sible to understand the uniqueness of personal subjective worlds and t
heir social (intersubjective) developmental roots.