There is at present much focus in ELT on describing and promoting teacher and learner agency. However, ELT as a professional field is concurrently characterised by an increasing orientation toward authoritative texts, particularly those imbued with authority at the transnational level. Global textbooks are a notable example, since they, along with global language testing and language policy, play an increasingly important role in determining teaching and learning practices across a range of different settings. Our focus in this paper is on how the authoritativeness of global textbooks is upheld in online promotional materials. Examining websites of three contemporary ELT textbook series, we analyse discourse strategies employed to legitimise the authoritative position of the textbooks and their publishers. We find that publishers legitimised their authority through strategic links to external forces (policy, testing), in this way foregrounding the universality of the textbooks. In contrast, the websites represented the agencies of teachers and learners only minimally, primarily as subordinate to the agency attributed to textbooks themselves. We conclude with a reflection on the need for applied critical scholarship in ELT that can offer practical alternatives and thus disrupt dominant notions of universality and the hierarchization of knowledge these are based on.