Abstract: Expression of induced resistance under field conditions will be influenced by both abiotic and biotic factors. Resistance can be induced by mutualistic symbioses such as mycorrhizal colonisation, as well as by pathogen and insect attack. In turn, inducing resistance can affect mutualistic symbioses, and lead to trade-offs in defence responses. In addition, the abiotic environment can also influence the expression of induced resistance. The plant’s attempts to orchestrate its responses to these multifarious environmental factors probably account for the incomplete disease or pest control achieved using resistance inducers. Providing our expectations of induced resistance are realistic, it will have an increasingly important role to play in crop protection in the future.