This article reviews research on peer feedback in second language (L2) writing published in the last decade (i.e. 2005-2014). We analyse first the theoretical underpinnings that have informed both peer feedback research and the pedagogical use of peer feedback in L2 writing instruction. We also provide a critical interpretation of existing peer feedback research and discuss seven important themes emerging from the literature, that is, (1) effectiveness of peer feedback compared with teacher and self-feedback; (2) benefits of peer feedback for feedback-givers; (3) computer-mediated peer feedback; (4) peer feedback training; (5) student stances and motives; (6) peer interaction and group dynamics; and (7) cultural issues in peer feedback. Next, we examine the contextual and methodological issues in peer feedback research and then conclude the article with implications for future research.