The innate immune system of both plants and animals uses immune receptors to detect pathogens and trigger defence responses. Despite having distinct evolutionary origin, most plant and animal immune receptors have a leucine-rich repeat (LRR) domain. The LRR domain adopts a slender conformation that maximizes surface area and has been shown to be ideal for mediating protein-protein interactions. Although the LRR domain was expected to be a platform for pathogen recognition, the NB-LRR class of plant innate immune receptors uses its LRR domain to carry out many other roles. This review discusses the domain architecture of plant LRRs and the various roles ascribed to this motif.