Underground Mathematics tells the story of subterranean geometry, a forgotten discipline that developed in the silver mines of early modern Europe. Seven case studies describe how an original culture of accuracy and measurement paved the way for technical and scientific innovations. Based on a variety of original manuscripts, maps and archive material, it recounts how knowledge was crafted and circulated among practitioners in the Holy Roman Empire and beyond. Specific chapters deal with the material culture of surveying, map-making, expertise and the political uses of quantification. By carefully reconstructing the religious, economic and cultural context of mining cities, Underground Mathematics argues that practical mathematics fruitfully interacted with the world of humanists, scholars and courts. In doing so, it contextualizes the rise of a culture of accuracy and quantification from 1500 to 1800. Subterranean geometry thus proves relevant to broader discussions in the history of science, technology, and knowledge.