While scientific literacy has historically focused on propositional knowledge, modern understandings of scientific literacy include procedural knowledge about how science works, including its social practices. Building on the work of others who have argued for the importance of textual literacy in scientific literacy, this chapter advances the notion that knowledge about scientific writing contributes to this holistic view of scientific literacy and that this is increasingly important in contemporary media environments. Beginning with the rationale for including textual literacy in scientific literacy, the chapter defines threshold concepts and describes four such threshold concepts that can function as portals toward deeper understanding of scientific writing: (1) scientific writing is central to scientific inquiry; (2) scientific writing is rhetorical; (3) scientific genres serve distinct purposes in scientific genre ecosystems; and (4) scientific writing and language are contested and dynamic. The chapter concludes by discussing the implications of this expanded understanding for scientific literacy and science communication, including common concerns around social and rhetorical views of science.