More than 400 achlorophyllous plant species in 87 genera are parasitic upon fungi, and exploit them as their principle source of carbon. With a few exceptions, most of these myco-heterotrophic plants are now thought to be 'cheats', stealing carbon and nutrients from the mycorrhizal associates of adjacent autotrophic plants. Most myco-heterotrophs are therefore considered to be epiparasitic on green plants. Both the ectomycorrhizal and arbuscular mycorrhizal symbioses have been invaded by myco-heterotrophic epiparasites. DNA analysis is revealing the identities of many of the fungal partners of myco-heterotrophs, and their exceptionally high specificity. Myco-heterotrophs have distinctive stable isotope signatures, which can be used to establish the dependence upon fungal carbon of green plants that are partially myco-heterotrophic.