Graduate teaching assistants (TAs) and the general education yet discipline-specific courses they often teach occupy a complex peripheral position in the university. This qualitative comparative case study investigated disciplinary TAs' identities and pedagogical strategies as they taught writing courses linked with disciplinary lecture courses at a large research university in the Western United States. Drawing on Wenger's (1998) theory of communities of practice, this article examines how TAs brokered students' encounters with disciplinary genres and how they helped students negotiate the tensions inherent in a general education curriculum. Focusing on two TAs, one from political science and one from art history, this study draws on interviews, classroom observations, and course documents. Findings suggest that the TAs positioned themselves in distinct ways in relation to their fields of study and the courses they taught--one as boundary crosser and the other as insider. The TAs' identities influenced how they brokered disciplinary genres and writing practices for students as well as how they mediated the tensions between discipline-specific and general education goals and contexts.