This research monograph investigates the immediate effects of peer feedback on text revisions and the long-term effects of peer feedback on writing performance. It also examines students& processing of peer feedback in revision and explores their perceptions of peer feedback. Peer feedback, an activity in which learners read others& drafts and make comments on them orally and/or in written mode, is widely employed in English as a foreign/second language (L2) writing instruction. Extensive studies investigating its effects have been conducted, and yet very few studies have examined how the effects take place and whether the effects sustain. To address the research gaps, this book reports a rigorous peer feedback intervention conducted during a semester-long College English course at a Chinese university. This research yields a deep understanding of the effects of peer feedback and provides an example of how a mixed methods approach can be employed in second language writing research. This book is a valuable research resource for researchers, practitioners and policymakers on an international scale.