[en] Neutron induced and spontaneous fission with neutron energies from 10^-2 to 2.10⁵ eV have been studied. Thermal neutron induced fission measurements in Pa²³¹, Th²³², Np²³⁷, U²³³, U²³⁵, Pu²³⁹ and Pu²⁴¹ are reported. Energy and mass distributions of heavy fission fragments due to the spontaneous fission of Pu²⁴⁰ are compared to the results obtained by thermal neutron fission of Pu²³⁹; the events observed with U²³⁶, Pu²⁴⁰, Pa²³² and Np²³⁸ are explained by the Bohr theory of fission channels. Ternary fission phenomena of U²³³, U²³⁵, Pu²³⁹, Pa²³¹ and Np²³⁷ induced by thermal neutrons are explained and compared to models of Carjan and Feather. (MDC)