This chapter presents a comprehensive overview of language curriculum materials, highlighting their central role in teaching and learning. Drawing on both theoretical perspectives and practice-based insights, it argues that CMs are not mere instructional supplements but integral components of the pedagogical process. A central contribution is the proposed Curriculum-Materials Adaptation Procedure (C-MAP), a systematic process for teachers to select principles, evaluate and adapt materials purposefully based on second language acquisition theories. The chapter emphasises the importance of principled, research-informed adaptations that respond to learner needs without undermining curricular intent. Through this lens, teachers are positioned as informed professionals who partner with curriculum materials to enact equitable, high-quality instruction in diverse language classrooms.