This chapter presents the theory and research related to the cognitive-interactionist perspective on TBLT. It examines how different kinds of tasks create opportunities for interaction that foster the processes involved in second language (L2) and thereby highlight the importance of social interaction for TBLT. It addresses the role that the negotiation of meaning and form play in the implementation of tasks and how negotiation is achieved through interaction, especially when there is corrective feedback. This chapter also examines to what extent how interaction fosters acquisition when tasks are performed. It concludes with an evaluation of this approach to investigating tasks, pointing out both its strengths and weaknesses.