This chapter is concerned with locating and defining writing in the context of communication in general, and in the more specific domain of human communication. It emphasizes the linguistic basis of all writing systems, examining their underlying characteristics, how their invention works as a representational resource and how they are intimately connected with social, material and cultural conditions. It clarifies basic concepts about writing, to establish some terms of reference and to find a language for subsequently talking about writing. Writing is seen as a system of visual communication that uses symbols that have a particular relationship to the world. The chapter underlines the materiality of writing as a visible language.