Did you know that just like humans, plants have an immune system. It helps them defend against parasites as diverse as fungi, bacteria, viruses, nematodes and insects. Over 75 years ago, an American scientist called Harold Floor studied how plants defend against parasites. He discovered that for each resistance gene in the plant, there's a matching gene in the parasite. She called this the gene for gene model. Floor's work was hugely influential. It helped guide breeding disease resistance in pretty much every crop plant. Later, scientists found out that plants have an immune system to defend against invading parasites. Floor's disease resistance genes turned out to be sensors that can detect the parasite and initiate an effective immune response. More recently, scientists realised that the plant immune system is much more complex than Floor's model indicates. Disease resistance genes appear to work together in intricate networks to deliver a robust immune response. These immune networks enable plants to detect and resist parasites more effectively for several reasons. First, networks are more robust and can still function even when one of the components fails. Second, networks enable plants to mount an optimal immune response when the environmental conditions are changing. Finally, networks are more adaptable, allowing plants to evolve more rapidly to keep up with constantly evolving parasites. This view of plant immunity has implications for plant breeding. We lose so much food to disease. If we can better understand how immune systems work, we can make plants more resistant to disease. And produce more food using less pesticide than we do today. From Floor's gene for gene model to today's systems view of plant immunity, a fundamental understanding of how plants fight parasites is vital. The study of plant immunity is just one example of how fundamental scientific knowledge can be applied to directly benefit society.