  In this paper, we review several important features of the out-of-equilibrium
dynamics of spin glasses. 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. We report in particular new
results on the sub-aging behaviour of spin glasses. We then discuss the
rejuvenation and memory effects observed when a spin glass is submitted to
temperature variations during aging, 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.
Finally, we report an investigation of the effect of small temperature
variations on aging in spin glass samples with various anisotropies which
indicates that this hierarchy depends on the spin anisotropy.

Disordered Systems and Neural Networks