This book comprehensively analyzes the development of interculturally blended third spaces by the second language learner, beginning with the linguistic and sociocultural imprints of the first language and culture on the mind and culminating in the proposal of a phase-model of the development of intercultural competence. The foundational analysis of L1-mediated constructs is followed by an analysis of forms interaction, concepts of identity and constructs of culture/interculture, thus shifting the object of analysis from the subjective to the intersubjective levels of construction and interaction. The focus of the book is on the gradual development of interculturally blended third spaces in the mind of the learner as genuinely new bases for construction. This book takes an interdisciplinary approach, drawing on research in cultural psychology, linguistic anthropology, critical theory, language acquisition and second language learning and shows how culture and interculture need to be emphasized as an integral part of second language learning.