Bernard Bolzano (1781-1848, Prague) was an outstanding thinker and reformer, far ahead of his times in many areas, including philosophy, ethics, politics, logic, theology and physics, and mathematics. Aimed at historians of mathematics, philosophy, ethics and logic, this volume contains the first English translations of some of his most significant mathematical writings, which contain the details of many celebrated insights and anticipations: clear topological definitions of various geometric extensions, an effective statement and use of the Cauchy convergence before it appears in Cauchy's work, remarkable results on measurable numbers (a version of real numbers), on functions (the construction of a continuous, non-differentiable function around 1830) and on infinite collections.