The pioneering framework I propose for the analysis of the foundations of human language – the Grammar of the Body – is inspired by sign language. My main aim is to create a body-based model of linguistic compositionality and to provide clues of its evolutionary origins.Instead of analysing sign language (and language generally) from the perspective of mental categories, the radical approach I introduce here analyses language from the outside in, from the physical articulators of the face, hands, and body in sign language, to the grammatical structures they manifest. This new approach capitalizes on the discovery that gestures of each articulator make a meaningful contribution to the whole corporeal display, and yield a hierarchy from small to large in both body and grammar domains: hands/words > head and face/phrasal intonation > torso/discourse perspective. I hypothesize that the corporeal base of compositionality has deeper evolutionary roots in the emotional face and body displays of humans and our closest living relatives, chimpanzees.The multi-disciplinary methodology I adopt will incorporate linguistic analysis of established and newly emerging sign languages with artistic manipulation of language form, and allow us to trace the origins of the system in emotional displays of both humans and apes.My central goal – determining the basis and structure of compositionality in human language – and the unconventional methodological approaches it exploits combine to make this an extremely ambitious proposal with potentially wide-reaching ramifications in the humanities and social sciences.