Jacob Bernoulli (1654-1705), founder of Basel's dynasty of mathematicians, left a relatively small body of correspondence for posterity. Published here for the first time are all 50 preserved letters sent to or by Jacob Bernoulli, and documentary evidence is presented of some l00 further letters no longer extant. The correspondence with Leibniz takes up the bulk of the volume and is also the most substantial scientifically. Topics range from Bernoulli's theories of elasticity and probability, to Leibniz' "Dynamik", to the integration of algebraic functions, to controversies over differential calculus and calculus of variations. The exchange offers rare insights into the personal histories and working habits of these two correspondents. Science politics dominates the brief but intensive correspondence (1700-01) with Geneva's Nicolas Fatio de Duillier, a leading exponent of Newtonian mathematics. Their letters broach Leibniz' claim to mathematical leadership, professional disputes between the brothers Jacob and Johann, and Fatio's theory of gravitation. Bernoulli's letters to teachers and friends, and business letters to Otto Mencke, publisher of Acta Eruditorum, shed further light on the until now little-researched life of Basel's famed mathematician.