This chapter introduces the book’s key concepts, including systematics, Eastern Africa, prehistory, stone tools, and guidebooks. What we call things matters. Names can clarify, confuse, or do both simultaneously. Finding names for prehistoric stone tools poses special difficulties. When archaeologists unearth ceramics or metal tools, we do so from sediments no more than a few thousand years old – relatively recently on a geological timescale. As a result, we have familiar household words for ceramics (e.g., bowl, plate, jar) and metal implements (e.g., axe, knife, nail). Stone tools, in contrast, range in age from the ethnographic present to more than three million years ago. Few people make and use stone tools any longer, and for this reason we lack subject-specific common words for them. Instead, we borrow words for Industrial Era metal tools (e.g., scraper, pick, awl). In developing terms for stone tools, the nineteenth- and early twentieth-century archaeologists who developed the artifact typologies we still use today relied on their intuition, but those archaeologists’ intuitions about stone tools and their functions reflected their experience excavating artifacts, not making or using them or observing others who did. Yet archaeologists have been reluctant to reform these stone tool systematics. We cannot blame their reluctance on sloth. Archaeologists are among the world’s hardest-working scientists; nobody looking for a life of leisure becomes an archaeologist. Nor can we blame ignorance, for critiques about theory and method in stone artifact analysis have a long history and have grown increasingly trenchant (e.g., Shea 2011b, Holdaway and Douglas 2012, Dibble et al. 2017). If the explanation for archaeologists’ reluctance to reform stone tool systematics remains an enigma, the need for such reform has become ever more pressing, and no more so than in Eastern Africa. Eastern Africa provides unique fossil evidence about long-term patterns in human evolution. Even so, Eastern Africa’s lithic record makes only a fraction of its potential contribution to African prehistory and to human origins research. Why is this so?