[en] Electron-impact ionization of ions is one of the most fundamental processes in every kind of plasma. Especially in high-temperature plasmas-whether in laboratory (nuclear fusion) or in astrophysics (atmosphere of stars)-atoms become ionized into multiply-charged ions by electron impact. The main purpose of authors' investigations is to unravel the contributions from different ionization mechanisms-like direct ionization (one-step process), excitation-autoionization (two-step process) and inner-shell Auger processes to the cross sections of single and multiple ionization of highly-charged ions. As the experimental database is still rather small, theoretical cross sections are often used for the calculation of different plasma parameters. Cross sections for ions with an outer 4f shell are usually small and experimental data is needed in order to test theories in that region. In the present study, the authors investigate the ionization of praseodymium ions, where cross section data has not been available up to now