Plants show physiological and morphological responses to a range of physical and chemical factors known as ‘elicitors’. These responses have been considered as defence reactions ‘elicited’ by the plants’ biochemical factory to ensure their survival, persistence and competitiveness. Recently examples have been cited of elicitation in some fungal and bacterial cultures. Through a chronological survey, this Review considers examples of elicitors and elicitation and describes suggested mechanisms of elicitation in plants and microbial cell cultures. The majority of research in this field has been carried out on the plant systems using complex (undefined) biotic elicitors. Carbohydrates are the main class of compounds used as defined elicitors. This Review focuses on carbohydrates as compounds initiating a defence response in cell cultures. Physiological changes brought about on the plant and microbial cultures include expression of novel metabolites and overproduction of already known products. Recent reports confirming elicitation in microbial cultures are of potential importance, as the relative ease of fermentation and scale-up could open an opportunity for the introduction of useful novel metabolites as well as enhancement of commercially useful bioproducts. In this context, a sound knowledge of the elicitor molecules’ structure–function relationships and mechanisms of elicitation is essential.