Theory of nuclear fission: present status and prospects

General properties of nuclear fission are reviewed and related to our present knowledge of fission theory. For this purpose the basic reasons for the shape of the fission barriers are discussed and their consequences compared with experimental results on barrier shapes and structures. Special emphasis is put on the asymmetry of the fission barriers and mass-distributions and its relation to the shells of the nascent fragment clusters. Finally the problem of a dynamical description of fission and its relation to the question of viscosity is discussed. (auth)