Irwin Shapiro, the former Director of the Harvard-Smithsonian Center for Astrophysics, has had a very localized geographical career – all in Cambridge – but has wandered widely in research, from study of the core of the Earth, through remote-sensing exploration of the solar system, to observation of the most distant known objects in the universe. He also originated and carried out solar-system tests of the general theory of relativity. The common thread tying these various topics together is his use of radio or radar techniques in all of these efforts.