Abstract: Like all other organisms, ants can be afflicted by a large number of microbial parasites and pathogens. In response, ants have evolved a range of immune defenses. Here we review current knowledge of ant immune defenses, focusing on the genes, proteins and chemicals involved in ant innate immunity. Some pathogen recognition, signaling and effector molecules (such as antimicrobial peptides) have been described from a range of ant species in different subfamilies, but a very large number of innate immunity components remain to be identified. Secretions of the metapleural glands have special significance as an ant-specific immunity component. Chemically diverse substances from these glands are known to have antimicrobial properties and hence to play an important part in ant life. In addition to the molecular and chemical defenses of individual physiology, individual and group behavior patterns make substantial contributions to fighting disease. Examples of behavioral mechanisms contributing to disease resistance include parasite avoidance, active inclusion of antimicrobial plant resins into nest materials, and increased colony genetic diversity through polyandry, polygyny, or both. We propose that future research links immunity at the molecular level with the ecology of ants and their pathogens, and studies evolutionary mechanisms to yield a comprehensive understanding of ant immune defense mechanisms.