This textbook, now in its second English edition, is originally a translation of the G- man textbook “Rechnen für Lagerstättenkundler und Rohstoffwirtschaftler, Teil 1”, also translated into the Chinese and Russian languages. Compared to the previous English and German editions the chapters have been updated with new examples and in many cases amended. The textbook is intended for the economic geologist who deals with the evaluation of deposits at an early stage of development. Once an exploration project has reached the feasibility stage, the exact calculations that are necessary for a comprehensive te- nical and economic assessment will be performed by a team of geologists, mining engineers, metallurgists, and economists. In the early stages of exploration, however, any evaluator of deposits must be able to cover the whole spectrum himself. Since only order of magnitude parameters are available at this early stage, the c- culations can only yield order of magnitude results. Precise calculations would even be misleading, since the evaluation does not yet aim at accurate economic assessment but at making the right decision: should the investigation be abandoned or should it be continued at higher costs and with more detailed methods.