Swift heavy ions with energies of about 5 MeV/u cause a high energy deposition into solid targets. As a consequence first the electronic system receives energy and afterwards the energy is transferred to the atomic system by electron phonon coupling or Coulomb repulsion. After a short introduction of what is denoted ion track, different approaches for investigating the ion track formation are presented. Typical experimental data corresponding to these approaches are discussed with respect to the thermal‐spike and Coulomb‐explosion models. © 2004 American Institute of Physics