Peer review is a complex collaborative activity, which may engage English language learners in reading, writing, listening, and speaking and carry many potential benefits for their language learning (Hu, 2005). While many research studies focused on peer review practices of adult language learners in academic settings in the USA or abroad in language classes (Grami, 2010; Zhao, 2010), little attention was paid to adolescent L2 writers participating in peer review in face-to-face K-12 and online contexts. This multiple case study aimed at describing and explaining peer review practices of four adolescent ELLs in face-to-face and online contexts from the ecological perspective. In particular, I aimed at exploring (a) four adolescent ELLs' perceptions of peer review in face-to-face and online contexts, (b) affordances they chose to employ during peer review in face-to-face and online contexts, and (c) revisions the participants chose to make due to peer review in face-to-face and online contexts. The multiple observations, semi-structured interviews, researcher's and participants' e-journals, and written artifacts yielded data for within-case and cross-case analysis. The findings of the study afforded situating adolescent ELLs' peer review practices in the face-to-face and online contexts as a part of L2 literacy, redefining L2 literacy and peer review in L2, and discussing the important role of peer review in adolescent ELLs' literacy development. The implications of the study provided teachers with suggestions on how to enhance adolescent ELLs' peer review practices. Further, I elaborated on the lessons learned about technology use for peer review in K-12 contexts. Finally, I addressed possible future research directions based on the findings of the study. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]