  The study of fluctuation-induced transport is concerned with the directed
motion of particles on a substrate when subjected to a fluctuating external
field. Work over the last two decades provides now precise clues on how the
average transport depends on three fundamental aspects: the shape of the
substrate, the correlations of the fluctuations and the mass, geometry,
interaction and density of the particles. These three aspects, reviewed here,
acquire additional relevance because the same notions apply to a bewildering
variety of problems at very different scales, from the small nano or
micro-scale, where thermal fluctuations effects dominate, up to very large
scales including ubiquitous cooperative phenomena in granular materials.
