In the last couple of years, open educational resources (OER), including open textbooks, have attracted considerable attention. So far, much of the discussion on open textbooks has focused on their putative economic benefits and the hope that these resources will help increase access to education, in particular for low-income, minority and other at-risk students. However, a focus on end-user access overlooks the structural and structuring nature of information technology, that is, how technology is shaped by social forces and vice versa. Drawing on scholarship concerned with infrastructure studies, the social shaping of technology and more recent studies on materiality, this research project analyzes open textbooks in terms of the new kinds of institutional arrangements, labor organizing and knowledge practices they make possible. Rather than isolated components or behaviors, I focus on the socio-technical systems of production, circulation, and consumption that constitute the open textbook infrastructure - the combination of software, institutions, and people that collectively produce textbooks and knowledge claims emerging from the OER ecosystem. Using OpenStax (https://openstax.org) as a case study, I propose an analytical framework that links together institutional structure, technical infrastructure, knowledge production, and pedagogy. The purpose of this presentation is twofold: first, to uncover the types of behavior the OpenStax platofmr presumes and engenders, and, second, to show how paying attention to infrastructure and materiality might help us theorize emerging technologies and the practices surrounding them in a way that recognizes their material, local and situated nature.