Galileo Galilei is a central figure of the scientific revolution of the modern age. His inventive genius and urge to discover are world-renowned, the debate with the church dictates Galilei''s image until today. The author presents a biography on Galilei''s work and achievements, which summarises the research findings so far and re-evaluates them. There are no anecdotes or life stories. It focuses on Galilei=s role in revolutionising the worldview in the 17th century, as well as the meaning of science at his time. This informed biography presents him for what he was, an outstanding explorer and inventor of the early modern age.