 Galileo Galilei (1564–1642) has always played a key role in any history of science, as well as many histories of philosophy. He is a—if not the—central figure of the Scientific Revolution of the seventeenth century. His work in physics (or “natural philosophy”), astronomy, and the methodology of science still evoke debate after more than 400 years. His role in promoting the Copernican theory and his travails and trials with the Roman Church are stories that still require re-telling. This article attempts to provide an overview of these aspects of Galileo’s life and work, but does so by focusing in a new way on his arguments concerning the nature of matter.