Resistance of plants towards potential pathogens is regulated by a variety of different local or systemic defence mechanisms which are either constitutively active or inducible upon challenge with a pathogen. Based on the knowledge acquired in studies on the molecular and biochemical mechanisms underlying especially different natural induced resistance phenomena, chemical inducers of resistance, derived both from plants or microorganisms or generated synthetically have been characterised and used to improve plant health. This article gives an overview on the present knowledge on resistance inducers and points to possible applications in the future.