Plants resist herbivorous insects and pathogens by employing specialised metabolites as chemical defences. In the case of constitutively present activated defences, an inactive precursor is stored and activated upon damage or attack by biotic stressors releasing high amounts of toxic and bioactive products. Glucosinolates are a group of defence compounds found in cruciferous vegetables. They consist of a nitrogen‐ and sulfur‐containing core structure and an amino acid‐derived, variable side chain. Enzymatic activation of glucosinolates further amplifies their chemical diversity, as one glucosinolate can generate different bioactive metabolites. These serve diverse functions in plant–insect and plant–pathogen interactions. Insects, however, have evolved many creative adaptations to avoid toxic glucosinolate‐derived metabolites. For humans, glucosinolates and their activation products have many beneficial health effects and promising applications in sustainable agriculture.