Secondary beams of radioactive ions at high energies are used at GSI to explore the nuclear structure of exotic nuclei. This report concentrates on the investigation of halo nuclei located at the neutron dripline. Relevant reaction mechanisms such as nuclear and electromagnetic break--up are discussed together with the nuclear structure information that can be deduced.

PACS numbers: 25.60.--t, 24.70.Ef, 27.20.+n