The aim of this dissertation is to describe how a group of L2 doctoral students in the natural sciences used online peer review in a research writing course. Inductive analysis was used to categorize the kinds of review comments that 11 course participants gave and received. In another study, three students' revised texts were analyzed in detail to see how they used peer comments. To explore students' perceptions of using the PR activity, pre and post course interviews were inductively analyzed. Findings were interpreted using Vygotskian constructs of learning in order to see where mediation likely occurs.