This fourth volume in "The Works of Jakob Bernoulli" centers on "Positiones de Seriebus Infinitis" whose five sections were defended from 1689 to 1704 by Bernoulli's students in dissertations. It represents what was probably the first systematic investigation of the summation of infinite series. In notes supplemental to the dissertations (Epimetra) contemporary questions in mathematics, the natural sciences and philosophy are addressed. In four journal articles, Bernoulli applies his theory of series methods to classic problems in Cartesian geometry as well as to the computation of compound interest. Furthermore, thirty preliminary papers (Meditationes) on Bernoulli's theory of series, taken from his scientific diary, appear here in print for the first time, as does his Vice-chancellor speech of 1701 tracing the study of cycloids. The paper illuminates Bernoulli's "modern" views on scientific methodology. Editor and famed French mathematician André Weil places Bernoulli's work on the theory of series on a broad evolutionary curve that extends from Oresme and Cusanus through Mengoli, Mercator, James Gregory and Wallis to the consolidation of the field by Euler and Abel.