In light of the growing agreement on the critical impact that materials can have on teaching and learning, classroom-based research on materials use in natural educational contexts has become increasingly urgent. This study aims to explore language teachers' use of instructional materials in classroom settings. Drawing on the analysis of materials, interviews, and lesson observations from cases of three Chinese English as a foreign language (EFL) teachers and their six students, this study identified six interactive processes of materials use, based on which teachers' pedagogical reasoning that enabled each process of materials use was unpacked. Through the theoretical lens of Keller and Keller's anthropology of knowledge and Wartofsky's categorization of artifacts, this article unraveled the relationship between teacher knowledge and practice in materials use and disentangled the multilayered roles of curriculum materials. The findings not only contribute to the conceptualization of materials use in language education but also suggest effective ways of enhancing the inservice professional development through materials use and development in natural educational contexts.