The Vygotskyan sociocultural approach to human development and cognition marked a new direction in psychology and created new, distinctive avenues for exploring fundamental matters of the mind. The complexity, diversity, and multilayered meaning of Vygotsky's formulations have in the history of psychology triggered scholastic debate, which has focused on the clarification, implications, and extension of the core explanatory constructs of his framework—mediation and internalization. The aim of this review is to offer a contemporary logico-semantic rereading of Vygotsky's formulations of these constructs with an emphasis on speech and, in particular, its dual mediatory role as a primary mediational means and a mediating process. Vygotsky's less renowned, and rather incomplete, propositions on the types of internalization are revived and examined in relation to the ontogenetic formation of speech. In this critical analysis, some ambiguous conceptual links between the notion of internalization types and the transformation of social speech into private speech and inner speech are explicated, debated, and refined. By addressing these conceptual links, the present examination extends the sociocultural account of semiotic mediation. The interpretations proposed highlight the logical cohesion and enhance the comprehensibility of Vygotsky's theoretical stance on human development.