  The dynamics of steps on crystal surfaces is considered. In general, the
meandering of the steps obeys a subdiffusive behaviour. The characteristic
asymptotic time laws depend on the microscopic mechanism for detachment and
attachment of the atoms at the steps. The three limiting cases of step-edge
diffusion, evaporation-condensation and terrace diffusion are studied in the
framework of Langevin descriptions and by Monte Carlo simulations.
