[en] Formation of ⁹⁹Tc in nuclear reactors and the fate of Tc in reprocessing plants are described. ⁹⁹Mo/^99mTc radionuclide generators for use in nuclear medicine, the production of ⁹⁹Mo, the importance of nuclear purity control and the selection of suitable compounds of Tc are discussed. The ways by which Tc may enter the environment, the dissolution of TcO₂ and the different migration and sorption behaviour of Tc(IV) and Tc(VII) are explained and the importance of the interaction of Tc with organic compounds is emphasized. (orig.)