The Galactic Cosmic Rays contain a sample of matter from elsewhere in the galaxy. It is a relatively recent sample (\sim 10⁷ years old) and contains information on the source material and conditions of confinement and transport in the galaxy. Unraveling the astrophysics of the cosmic rays has been underway for half a century, but major progress has been made in the last decades. The current state of our astrophysical knowledge of cosmic rays is reviewed in different energy regions, with particular attention to the implication of recent isotopic composition measurements at low energy. Extrapolating to higher energy delineates some of the experimental challenges facing the field in the future.

PACS numbers: 96.40.--z, 98.70.Sa