Inspired by Vygotsky's sociocultural theory and Storch's framework of peer interaction, this study investigated the nature and outcome of peer interaction in EFL (English as a foreign language) learners' peer review and revision activities. During two 16-week semesters, 32 lower-intermediate learners participated in an Advanced Writing university course. Each of the learners wrote and revised six one-paragraph writing assignments and exchanged peer negotiated feedback in pairs. The qualitative analysis of their recorded dialogues revealed that although the learners were nearly at the same proficiency level, they adopted a variety of patterns of interaction including collaborative, expert/novice, dominant/dominant, and dominant/passive. Collaborative and dominant/passive patterns were the most and the least frequent patterns, respectively. The analysis of feedback types indicated that the collaborative pairs exchanged the highest number of feedback in total and could extend their focus to content and organization of the texts more than the other pairs. The lowest number of feedback was observed in pairs adopting a dominant/passive pattern of interaction. Further analysis showed that while collaborative learners succeeded in revising the majority of their errors correctly and had the greatest short-term writing development, the passive learners failed at both to a large extent. These findings are discussed drawing on relevant theoretical and practical literature, and implications for second language (L2) writing instructors and researchers are suggested.