Theories with gauge-mediated supersymmetry breaking provide an interesting alternative to the scenario in which the soft terms of the low-energy fields are induced by gravity. These theories allow for a natural suppression of flavour violations in the supersymmetric sector and have very distinctive phenomenological features, Here we review their basic structure, their experimental implications, and the attempts to embed them into models in which all mass scales are dynamically generated from a single fundamental scale, (C) 1999 Elsevier Science B.V. All rights reserved.