The first decade of the new millennium should see the first direct detections of gravitational waves. This will be a milestone or fundamental physics and it will open the new observational science of gravitational wave astronomy. But gravitational waves already play an important role in the modeling of astrophysical systems. I review here the present state of gravitational radiation theory in relativity and astrophysics, and I then look at the development of detector sensitivity over the next decade, both on the ground (such as LIGO) and in space (LISA). I review the sources of gravitational waves that are likely to play an imp rtant role in observations by first- and second-generation interferometers, including the astrophysical information that will c me from these observations. The review covers some 10 decades of gravitational wave frequency, from the high-frequency normal odes of neutron stars down to the lowest frequencies observable from space. The discussion of sources includes recent developments regarding binary black holes, spinning neutron stars, and the stochastic background.