This study explores learners’ online peer review practices during a four-week second language writing project. The project was developed at the college level, in a multi-section upper-level Spanish writing course. Using theories relevant to second language acquisition and second language writing the goals of the study were multiple: (1) to identify the types of comments students used and explore peer review in terms of the givers’ and receivers’ roles, (2) to examine students’ attitudes and self-perceptions about peer review, and (3) to develop an understanding of how students’ attitudes and self-perceptions may influence their feedback-giving procedures. The three goals were addressed using different methods of inquiry, and the findings obtained in the first phase guided the analysis that took place during the second phase. In the quantitative phase, the analyses of data sources (e.g., feedback comments given and received and students’ written drafts) show that giving feedback is a better predictor of final performance than receiving feedback. This principle of learning by reviewing is most evident when students offer feedback that identifies problems, gives a justification, or explains positive elements in the peers’ text. The qualitative phase builds on the quantitative results: it zooms in to the role of the feedback giver to further explore participants’ attitudes and perceptions towards peer review. The analyses of data sources (e.g., pre-study questionnaire, participants’ interviews and peer review simulation activity, and the teacher-researcher reflective journal) show that students do self-position themselves into a specific feedback-giving role. Moreover, the study also confirms that students’ perceptions regarding their attitudes and the comments they give to peers accurately corroborate their actual peer review performance. By combining both methods of inquiry, quantitative and qualitative methods, this study further examines the specific procedures that two case study students follow when offering feedback to a peer. In particular, the procedures for offering problem identification, suggestion, and explanation of the praise comments are analyzed in detail. The results are further interpreted through the lenses of the feedback-giving roles assumed by each of the case study students. Based on the overall findings, the study suggests broadening the notion of feedback: from a unilateral perspective in which comments are addressed from feedback givers to receivers, to a multilateral perspective in which the comments offered are meant to benefit both feedback givers and feedback receivers. The study ends with pedagogical implications for second language learning, implications for the field of second language acquisition, and perspectives for future research.