 bark beetles and fungi form mutually beneficial relationships known as ectosymbiotic associations. These associations vary widely in terms of the level of dependency, the mode of transmission, and the environmental factors involved. They also differ in terms of the number of partners involved, with some being composed of multiple partners. Evolutionary processes, including phylogeny, abiotic environment, and interactions within the biotic community have played a role in shaping these associations. This article was offered by Diana L. Six.