A teacher's response is a key element in students' motivation and achievement in college writing courses. The area of Written Corrective Feedback (Ferris, 1999; Truscott, 1996) has been extensively studied in second language (L2) writing scholarship, but that research, to date, has not elucidated why individual instructors respond to students' papers in the ways they do, and few researchers have addressed the question of the sources of those differences, as revealed in commentaries. To pursue this question, the present study is an investigation of teachers' beliefs to establish an epistemological base for understanding their responding practices and to expand the scope of research on teachers' belief systems. Drawing upon the acts of teachers' beliefs as filters, frames, or guides (Fives & Buehl, 2012) and multi-level contextual factors in an instructional system (Buehl & Beck, 2015) as conceptual frameworks, this multiple-case study is an examination of the pedagogical beliefs underlying college writing instructors' decisions in providing their comments to guide students' essay revisions. Specifically, the beliefs espoused by four teachers of college writing courses for multilingual students were explored in relation to their commenting practices, with reference to three teacher-related factors: their first language, their focus in guiding students' revision processes, and their instructional choices between text-based and screencast comments. Data sources included teachers' written and audio-visual comments on students' drafts and semi-structured interviews with teachers featuring stimulated recalls to investigate their self-reported beliefs and actual commenting practices. Findings reveal how the teachers' beliefs were manifested in their commentaries as they made strategic choices in terms of their first language, focus in providing guidance, and choice between mono-modal text-based and multimodal computer-mediated comments, suggesting an empirical model to explain the relationship between teachers' beliefs and practices in providing comments to L2 student writers. The study provides pedagogical implications for L2 writing teachers and teacher educators with emphasis on a holistic approach to writing teachers' reflective practices as well as theoretical implications for further research on writing teachers' pedagogical beliefs and practices and two modes of teacher commentary. [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.]