How language learners and teachers actually use "pedagogical materials" in classrooms is a 'groundbreaking' subject of applied linguistics inquiry (Tarone, 2014, p. 653), referred to in this research agenda article as "materials use." We begin with a theoretically-oriented overview of language education scholarship on pedagogical materials (henceforth "materials"). Then, we focus on seven qualitative research tasks across three thematic areas, namely "materials use" and: (A) language pedagogy, (B) classroom interaction, and (C) language diversity, culture, and power. The first section on pedagogy outlines research tasks on: (1) the roles of materials in classrooms, (2) the influences of materials on practicing educators' expertise, and (3) how language teacher education programmes address materials use. The second section on classroom interaction proposes inquiry into: (4) polysemiotic patterns of materials-in-interaction, and (5) the expected and unexpected outcomes of materials regarding students' target language use. The third section focuses on: (6) teachers' and learners' responses to diverse linguistic varieties and cultures represented in materials, and (7) instructional materials used in language policy and planning endeavours. Throughout this article we reference interdisciplinary connections to curriculum studies, cultural studies, sociology, and materials scholarship in general education. The seven research tasks are critical next steps for understanding "materials use"--a vast new field that promises to advance language education practice and theory.