Minimizing losses to pests and diseases is essential for producing sufficient food to feed the world's rapidly growing population. The necrotrophic fungus Botrytis cinerea triggers devastating pre-and post-harvest yield losses in tomato (Solanum lycopersicum). Current control methods are based on the pre-harvest use of fungicides, which are limited by strict legislation. This investigation tested whether induction of resistance by b-aminobutyric acid (BABA) at different developmental stages provides an alternative strategy to protect post-harvest tomato fruit against B. cinerea. Soildrenching plants with BABA once fruit had already formed had no impact on tomato susceptibility to B. cinerea. However, BABA application to seedlings significantly reduced post-harvest infection of fruit. This resistance response was not associated with a yield reduction; however, there was a delay in fruit ripening. Untargeted metabolomics revealed differences between fruit from water-and BABA-treated plants, demonstrating that BABA triggered a defence-associated metabolomics profile that was long lasting. Targeted analysis of defence hormones suggested a role of abscisic acid (ABA) in the resistance phenotype. Post-harvest application of ABA to the fruit of water-treated plants induced susceptibility to B. cinerea. This phenotype was absent from the ABA-exposed fruit of BABA-treated plants, suggesting a complex role of ABA in BABA-induced resistance. A final targeted metabolomic analysis detected trace residues of BABA accumulated in the red fruit. Overall, it was demonstrated that BABA induces post-harvest resistance in tomato fruit against B. cinerea with no penalties in yield.