  We review the time evolution of wavepackets at the metal-insulator transition
in two- and three-dimensional disordered systems. The importance of scale
invariance and multifractal eigenfunction fluctuations is stressed. The
implications of the frequency- and wavevector-dependence of the diffusion
coefficient are compared with the results of numerical simulations. We argue
that network models are particularly suited for the investigation of the
dynamics of disordered systems.
