Interdisciplinary collaborations to help students compose for discipline-specific contexts draw on multiple expertise. Science, technology, education, and mathematics (STEM) programs particularly rely on their writing colleagues because (1) their academic expertise is often not writing and (2) teaching writing often necessitates a redesigning of existing instructional materials. While many writing studies scholars have the expertise to assist their STEM colleagues with such tasks, how to do so--and, more fundamentally, how to begin such efforts--is not commonly focused on in the literature stemming from these collaborations. Our article addresses this gap by detailing an interdisciplinary Writing in the Disciplines (WID) collaboration at a large, public R1 university between STEM and writing experts to redesign the university's introductory biology writing curriculum. The collaborative curriculum design process detailed here is presented through the lens of wayfinding, which concerns orientation, trailblazing, and moving through uncertain landscapes according to cues. Within this account, a critical focus on language--what we talk about when we talk about writing--emerges, driving both the collaboration itself and resultant curricular revisions. Our work reveals how collaborators can wayfind through interdisciplinary partnerships and writing curriculum development by transforming differences in discipline-specific expertise into a new path forward.