The works from Daniel Bernoulli's youth contained in this first volume of his Collected Works bear witness above all of his versatility; they deal with subjects as different as physiology, formal logic, mathematical analysis, hydrodynamics and positional astronomy. Daniel Bernoulli's contacts with Italian scientists gave rise to several controversies. The present volume documents both sides in each of these debates, which culminated with the publication of Bernoulli's first book Exercitationes mathe- maticae in 1724. The discussions with the renowned mathematician Jacopo Riccati on second-order differential equations and on the Newtonian theory of the out-flow of fluids from vessels deserve particular interest. A third group of texts goes back to the time Bernoulli spent at the newly- founded Academy of Sciences in St. Petersburg, where he had been appointed in 1725. There he worked out two more contributions to physiological research - on muscle movement and on the blind spot in the human eye - as well as his only paper in positional astronomy. This last work - suggested by a prize question of the Paris Acadmie des Sciences - became the occasion for a vehement conflict; the present volume documents these "Znkereien" (squabbles) and also reproduces three competing treatises. To complete the documentation of Daniel Bernoulli's work on physiology, the volume also includes his academic ceremonial speech De Vita of 1737, where he sketches for the first time the circulation of the work done by the human heart, and its elaboration by Bernoulli's student Daniel Passavant.