This paper presents writing as an extended cognitive system comprised of brain, body, and the material form that is writing. Part I introduces the theoretical framework used for the analysis, Material Engagement Theory (MET), and the initial insights into writing systems gained by applying MET to Mesopotamian artifacts for numbers and writing. Part II discusses how writing as a material form has changed over time and why this material change reflects, accumulates, and distributes change in the behaviors and brains of (...) generations of writers. Part III explains why forms of writing used today are a visible form of language in being comprised of contrastive graphic features. Part IV argues against the idea that writing should be excluded from being considered as an extended cognitive system. On the contrary, considering writing from this perspective can provide new insights into the ways we use material forms—not just in writing but more broadly—to change our behaviors and brains, and their roles in intensifying and perpetuating those changes. (shrink)