All arthropods encounter potential pathogens and have an immune system that plays important roles in defense. Most immunological research focuses on model organisms, like fruit flies, and to some extent, mosquitoes. Fewer studies focus on agricultural pests (e.g. moths), natural enemies (e.g. wasps), or other vectors (e.g. fleas and kissing bugs, ticks). The goal of this PBT symposium is to stimulate communication among researchers who study the immune system of phylogenetically diverse arthropods. Our primary objective is to advance understanding of arthropod immunology by showcasing key concepts, novel study approaches, and comparative data.