Why We Gesture capstones three previous books—an inadvertent trilogy spanning 20 years—How Language Began (Cambridge University Press, 2012), Gesture and Thought (Chicago University Press, 2005) and Hand and Mind (Chicago University Press, 1992). In Why We Gesture the three merge into a single multifaceted hypothesis. It has many facets but is one hypothesis. To present it in its fullness is the purpose of the book. The integration itself—that it is possible—is part of the hypothesis. Integration occurs because of a central idea—implicit in the trilogy, explicit here—that gestures orchestrate speech. In simplest terms, this answers the implicit question of our title: to orchestrate speech is why we gesture. We gesture because we speak—not that speech triggers gesture but that gesture orchestrates speech; we can speak because we gesture, rather than we gesture because we speak. To present such a package takes time and an ordering of parts but the whole is the important thing, to be grasped as such, considered all at once and all together. To this end, brevity is a virtue, and I have held the book to the main points. My impression is that many readers know one book of the trilogy or the other, but few have read them all, let alone have worked out the conceptual framework they collectively create. This is hardly surprising: it has nowhere been spelled out as such. Why We Gesture does it for the reader. The hypothesis in all its facets is here in one place, rendered as briefly as I can manage without losing intelligibility and completeness. Moreover, Why We Gesture has uncovered connections that had earlier escaped notice —the integrative role of gesture-orchestrated speech is one (mentioned in passing in Gesture and Thought but now on center stage). Equal in importance and pervasiveness is the idea of “new” gesture-actions and how they differ from “old” action-actions, these last assumed widely as the core of gesture but that, if admitted, would decisively roadblock gesture-orchestrated speech. The principal new finding of the book is that much material coalesces naturally around these concepts.