Introduction - general outline and scope Time and Space - Italy just before and during Galileo's lifetime (economy, politics, culture, historical developments), landscapes and people Early Years (1564-1588) - the weight of solid bodies, la bilancetta Pisa - gravitational experiments (de motu) in this chapter as in all others following the structure is as follows: state of the art ante, Galilei´s results, (corresponce), impact Padova - telescope, astronomical discoveries Florence - further astronomical discoveries, first positioning to Copernicus, Saggiatore: further conflict potential Cosmological Excursion - world models, Anaximander, Ptolemy, Aristarch, Erastosthenes, Copernicus, Kepler Florence revisited - Dialogo and ist consequences, correspondence with Kepler Final Years - Discorsi Conclusions - importance of his contributions (discoveries, methodologies, scientific development, philosophy).