Insects primarily rely on innate immunity to defend against pathogens, and the recognition of pathogens by pattern recognition receptors (PRRs) to trigger immune responses. Lectins are widely present in animals and plants, and they bind to specific carbohydrates, glycoproteins, or glycolipids through their carbohydrate recognition domains (CRDs), thereby serving as crucial PRRs in insect immunity. Insect lectins mainly include C-type lectins and galectins which play multiple functions in the innate immune system. This review outlines the classification, structure, and evolutionary characteristics of insect lectins, with a focus on the functions of C-type lectins and galectins in the insect innate immune system, and briefly introduces the functions of insect lectins on growth. It is hoped that this review will inspire studies of host-pathogen interactions, and contribute to the improvement of microbial biopesticides targeting the immune system.