Communication and, indeed, our comprehension of the world in general are largely ordered by the number and measurement systems that have arisen over time. Numbers lend structure to human interaction by standardizing the language we use to interpret quantities and by helping us understand natural relationships between varying concepts. This book delves into the history of mathematical reasoning and the progression of numerical thought around the world. With detailed biographies of seminal thinkers and theorists, readers develop a sophisticated understanding of some of the most fundamental arithmetical concepts as well as the individuals who established them.