Symbiotic associations between mammals and fungi have been well documented and are widely regarded as vital to ecosystem functions around the world. Symbioses between birds and fungi are also ecologically vital but have been far less thoroughly studied. This manuscript is the first to review a wide range of symbiotic associations between birds and fungi. We compile the largest list to date of bird species reported to eat fungi (54 bird species in 27 families) and follow up with a discussion of these symbioses and suggestions for how future studies can determine the prevalence of associations between birds and fungi. We review the importance of fungi for cavity-excavating birds and show that at least 30 bird species in three families form varying levels of associations with fungi for cavity excavation. We also review the use of fungal rhizomorphs in nest construction and show that 176 bird species in 37 families use fungal material in their nests. All of these interactions have wide-reaching ecosystem implications, particularly in regard to fungal dispersal and biogeography, plant health, ecosystem function, bird nutrition/fitness and bird behaviour.