  In this paper, we review the general features of the out-of-equilibrium
dynamics of spin glasses. We use this example as a guideline for a brief
description of glassy dynamics in other disordered systems like structural and
polymer glasses, colloids, gels etc. Starting with the simplest experiments, we
discuss the scaling laws used to describe the isothermal aging observed in spin
glasses after a quench down to the low temperature phase (these scaling laws
are the same as established for polymer glasses). We then discuss the
rejuvenation and memory effects observed when a spin glass is submitted to
temperature variations during aging, and show some examples of similar
phenomena in other glassy systems. The rejuvenation and memory effects and
their implications are analyzed from the point of view of both energy landscape
pictures and of real space pictures. We highlight the fact that both approaches
point out the necessity of hierarchical processes involved in aging. We
introduce the concept of a slowly growing and strongly temperature dependent
dynamical correlation length, which is discussed at the light of a large panel
of experiments.
