This paper aims to clarify the meaning of the term `materials` in the context of English language teaching and define materials evaluation and selection to differentiate it from materials development and adaptation. On the basis of a literature review, the definition of `materials` is suggested in terms of their physical and functional aspects. In regards to a physical form, `materials` cover a coursebook, potential coursebooks, workbooks or activity books, supplementary teachers` books, resource books, reference books, audio cassettes, video cassettes, newspapers, journals, CALL software, CD-Roms, Internet web-site, email in addition to one-off materials, i.e. photocopied handouts prepared by teachers, `teach-yourself` materials, `home-study` materials, and `self-access` materials. With regard to functional aspects, materials are intended to facilitate learner`s language learning in any way. We have attempted to extend our perception of materials evaluation through the discussion of conceptual development in definitions of educational evaluation, and included the activity of selection as evaluation by considering its pragmatic value. Based on our recognition of definitions and relevant remarks in the literature, we propose the following definition of materials evaluation: Materials evaluation is a decision-making process, which may involve making a judgment about the success of certain materials through empirically valid and reliable ways of information collection and/or about relative merit of some competing materials through a systematic process of information collection with regard to users in particular circumstances (or findings of language learning research).