Arbuscular mycorrhizal symbioses have been an integral part of terrestrial ecosystems since the invasion of land by plants. Studies on the descriptions, phylogenetic relationships, and world-wide distributions date back to the late 1800s. By the 1950s, the basic systematic position of the fungi was known. By the early 1980s the underlying functions of AM were documented. During the last decade, most research has focused on detailing the varying forms that AM functions could take as the species compositions environments and environment/species interactions varied. Research into the next century should begin to develop a better understanding of population genetics of the fungi and how those influence phylogeny and ecological functioning, a better evaluation of the subtle changes in ‘mycorrhizal functioning’ given the large divergence in environmental and biological interactions, and the ability to link mycorrhizal dynamics into the changing global conditions.