Based upon theories of computer mediated communication of Herring and Lemke and the work of genre scholars such as Askehave, Santini, and Devitt, this qualitative study explored how computer mediated communication shapes writing genres in an online classroom. Genre embodies the context and users' purpose for any textual communication. Through a case study of a graduate level online class, the study investigated students' experiences of the genres realized by their writing in the online classroom. The primary goal of the research study was to understand students' experiences of enacting the multiple writing genres in an online class. The research questions were: 1) What are the rhetorical situations for students' writing in an online classroom? 2) How do students acquire knowledge of the conventions of the multiple genres of online classroom writing? 3) What are students' experiences of enacting the multiple writing genres in an online classroom? Semi-structured transcribed interviews, field notes of online classroom observations, artifacts gathered from the online class, and questionnaire results were collected as data and interpreted by applying an inductive analysis. The online classroom is a multi-generic space where students are called upon to enact various writing genres, depending on the rhetorical situation of the learning activity, in order to perform the social practices of online education. Genre is a useful lens for exploring students' online writing practices because genres offer a means of accessing the ways language forms the experience of information and ideas. Since online classes immerse students in an environment of written text, online student writing illustrates evolving web genres in action. This changeable notion of genre suggests that opportunities exist within the online space for students to direct their own genre performances in ways that make sense for their computer mediated learning environment. The study revealed students' awareness of their own rhetorical choices through the enactment of particular writing genres online and how their writing was shaped by computer mediated communication. The online classroom has the potential to be an optimal space for students to engage in genre (re)formation shaped by the CMC medium of online learning. The results and analysis of the research may influence institutions to take a more informed approach to improving instructional practices online in general and writing practices online in particular.