This article reviews patterns of interaction (i.e. learner role relationships) in peer communicative tasks, and uses data collected from different tasks to explain what happens in peer interaction and its impact on the learning opportunities interlocutors create for each other. It proposes that, with L2 peer interaction gaining popularity in language classrooms, an in-depth understanding is needed of how learners relate to each other in paired dialogues to jointly build new knowledge. In particular, the view that learners will naturally collaborate with each other to complete tasks is challenged. Consequently, based on the discussion of previous studies and data from the present study, implications and suggestions for organizing effective peer interaction activities are explored.