Plants can get sick too. In fact, they get infected by all types of microbes and little critters. But plants have evolved an effective immune system to fight off pathogen invasion. Amazingly, nearly every single plant cell is able to protect itself and its neighbours against infections. The plant immune system gets switched on when one of its many immune receptors matches a ligand in the pathogen. As a consequence of a long evolutionary history of fighting off pathogens, immune receptors are now encoded by hundreds of genes that populate the majority of plant genomes. Understanding how the plant immune system functions and how it has evolved can give invaluable insights that would benefit modern agriculture and help breeding disease-resistant crops.