A long-term goal of community ecology is to identify spatial and temporal factors that underlie observed community structures. Ultimately, ecologists seek to relate community patterns to ecosystem processes and functions. Since the mid 1990s, ectomycorrhizal (ECM) research has been equipped with tools to identify and fully quantify the taxonomic diversity in below-ground ECM fungal communities in detail and address such questions. Many of the most important functions of terrestrial ecosystems, as well as interactions, between plants take place below ground and mycorrhizal fungi are among the key players in soil ecology. Here the rapidly increasing knowledge of ECM fungal community ecology is reviewed and the prospects discussed for elucidating processes that structure ECM fungal communities and the way in which such knowledge might be integrated with, and advance, the understanding of plant ecology and ecosystem processes.