Gaia is a mission to map the positions and determine the velocities of 1 billion stars in the Galaxy, in order to determine how it was formed and how it has evolved. Spectroscopy provides one component of the space velocities for 200 million objects, and, in addition, astrophysical information such as temperature and metallicity for the brighter 40 million stars in a large unbiased Galactic sample. Together the instruments on Gaia will transform our knowledge of the Galaxy. We describe here a sample of the science that will be done with Gaia concentrating on aspects in which the spectroscopy plays a central role. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html