When supporting student's writing process, teachers normally leave written comments on their papers. Teacher written comments represent a discursive genre that presents constant features, even though teachers and tutors usually do not receive specific training on them. Teacher written comments are a dialogic resource aimed at guiding the writing of students venturing into the learning of a new subject. In this sense, written comments are a genre oriented to the appropriation of another discursive genre on the part of the writer. Teacher written comments are a type of feedback resource that already has wide array of research in English both as a first and as a second language. The objective of this monograph is to present the main research developed in English on written comments and to propose an explanatory theoretical framework from the discursive genre theory. Current literature provides information on the linguistic, discursive, and rhetorical features that characterize written comments, as well as the reaction they produce in students. This paper conveys the idea that teacher written comments are a rich field of study that provides information on how a genre, in the dialogic writing process, favors learning of another genre.