  We attempt to give a bird's eye view of the physical mechanisms leading to
anomalous relaxation, and the relation of this phenomenon with anomalous
diffusion and transport. Whereas in some cases these two notions are indeed
deeply related, this needs not to be the case. We review several models for
stretched exponential relaxation (diffusion in traps, broad distribution of
relaxation times, two-step relaxation) and insist on the physical
interpretation to be given to the stretching exponent $\beta$. We then discuss
compressed exponentials which have been recently observed in a variety of
systems, from soft glassy materials to granular packs. We describe a model
where slow rearrangement events occur randomly in space and create long ranged
elastics strains, leading to $\beta=3/2$.
