Writing is widely recognized as fundamental to the construction and communication of scientific knowledge. Building on this relationship between writing and knowledge construction, writing‐to‐learn (WTL) activities have shown to be effective in many science classrooms, but have not been widely implemented at the postsecondary level. To address the lack of implementation, we investigated potential adopters of this pedagogy. Potential adopters, postsecondary faculty, are unique given the key role writing plays in their professional practice as researchers. Because of this unique feature and the fact that an instructor's theoretical orientation toward a construct impacts their instruction of that construct, an investigation of postsecondary faculty's conceptions of writing instruction is necessary to understand the way writing is being used in the postsecondary classroom. To this end, 33 STEM faculty across multiple disciplines and positions were interviewed about writing and its role in their classes. A phenomenographic analysis resulted in four faculty “types” consisting of unique combinations of concept and practice, organized according to compatibility with WTL. Profiles were built that describe unique conceptions, desired outcomes, and challenges for each type. These profiles provide an understanding of the relationship between faculty's conceptions and instructional practices regarding writing and lay the groundwork for understanding how writing is used in the postsecondary classroom.