Ion beams are unique tools in modern science and technology. They are used for the analysis and modification of materials and are applied in medicine and technology. In cancer therapy fast protons allow a precise tailoring of the radiation field to the tumour, thus maximising the tumour control probability and simultaneously reducing the risk of side effects. Modification of the structure of solids by ion irradiation results in local structures on nano-scale, e.g. high-tech filters having defined pore numbers and pore sizes are produced by high-energy heavy ion irradiation with consecutive etching. Electronic devices utilised in areas with high radiation level have to be tested for their radiation hardness. The devices are irradiated with accelerated ions to receive the same dose by high-energy ions as expected during their lifetime. For materials sciences the analysis of composition and structure of solids is of uppermost importance. Complex layered structures are analysed by ERDA (Elastic Recoil Detection Analysis). Investigation of art and archaeological objects has to be non-destructive. PIXE (Proton Induced X-ray Emission) allows elemental analysis without sampling of the object. Different applications of high energy ions will be presented.