Polyamines are ubiquitous amine molecules found in all living organisms. In plants, beside their role in signaling and protection against abiotic stresses, there is increasing evidence that polyamines play a major role in the interaction between plants and pathogens. Plant polyamines are involved in immunity against pathogens, notably by amplifying PTI (Pattern-triggered immunity) responses through the production of reactive oxygen species. In response, pathogens use phytotoxins and effectors to manipulate the levels of polyamines in the plant, most likely to their own benefit. It also appears that pathogenic microorganisms produce polyamines during infection, sometimes in large quantities. This may reflect different infectious strategies based on the selective exploitation of these molecules and the functions they perform in the cell.