The field of content area literacy instruction is shifting from a general understanding of literacy towards disciplinary literacy. Much of the work in the field of disciplinary literacy has focused on reading, while writing has often been overlooked. This article summarizes the findings of a qualitative case study of two preservice teachers as they experienced a unit of study during a Reading in the Content Areas course. Described in the article is how the unit of study as a writing assignment encompasses three aspects of disciplinary literacy: (1) discourses and practices in disciplinary learning and literacy, (2) identities and identifications in disciplinary learning and literacy, and (3) knowledge in disciplinary learning and literacy. Results found the unit of study enhanced preservice teachers' knowledge of their discipline and writing instruction. The unit of study approach to writing instruction may offer literacy educators a way to engage preservice teachers in writing specific to their discipline. (Contains 5 figures.)