This chapter discusses the critical features of the new activity theoretic, social constructionist practice of developmental learning, and shows how this activity is not one of applying Vygotsky instrumentally to specific areas such as education and therapy, but rather one of transforming his work via a nonepistemological, therapeutic tool-and-result modality. A nonepistemological, therapeutic modality might seem to be a contradiction in terms, given how thoroughly cognitized psychotherapy and other approaches to human subjectivity, including psychology and psychiatry, have become. Vygotsky's views on language and thought, that is, speaking and thinking challenge what is a mentalistic and representationalist conception of language, for he claimed that speaking does not express, but completes, thinking. Vygotsky believed that 'a child's greatest achievements are possible in play' because the kind of free play young children engage in creates a zone of proximal development (ZPD). Play differs from nonplay in freeing us from situational constraints.