This book is about the young child's intentionality and the importance of this intentionality for explaining language acquisition. Intentions are expressed in actions, and they are constructed by interpreting the actions of others. The cognitive, social, and emotional developments during the first three years of life lead to the elaboration of intentional states, and this elaboration involves the representation of more elements, roles, and relations. The elaboration further involves the child coming to be able to recall the past and anticipate events in the future that other persons cannot yet know. The increasingly elaborated and discrepant intentional states require that the child learn more of the language to express them. The Intentionality Model presented here builds on the child's engagement in a world of persons and objects, the effort that learning the language requires, and the essential tension between engagement and effort that moves language acquisition forward. According to this first person child-centered perspective, children learn language in acts of expression and interpretation; they work at acquiring language; and all aspects of a child's development contribute to this process.