$\frac{1}{f}$ noise and other slow, nonexponential kinetics in condensed matter

Fluctuations in resistivity with an approximately $\frac{1}{f}$ spectrum are found in most conducting materials. Some of the detailed mechanisms, which turn out to be quite diverse, are explored in this review. Several new techniques are explained. Various theories are critically examined. Some connections with other widespread phenomena, such as highly nonexponential dielectric relaxations, are briefly investigated.