Plants collaborate with many micro-organisms in the rhizosphere to form mutualistic associations. One of the best examples is the mycorrhizal symbio­ sis between plants and fungi. Here, fungi support plants with mineral nutri­ ents and other services and the fungi, in turn, receive photosynthates from the autotrophic plants. Mycorrhizal associations are common in almost all eco­ systems and 80 % of all land plants associate with these mutualistic soil fungi. There is an increasing awareness among biologists, ecologists and mycolo­ gists that mycorrhizal associations need to be considered in order to under­ stand the ecology and evolution of plants, plant communities and ecosystems. In the last decade, many advances and breakthroughs have been made in mycorrhizal ecology. We aim to summarise these advances in this Volume, with special emphasis given to the ecological function of the mycorrhizal symbiosis. This Volume is divided into six sections. The first section gives an intro­ duction to the mycorrhizal symbiosis and discusses the progress that has been made in understanding the ecological function of this association. The second section deals with the eco-physiology of mycorrhizal plants. It also covers the influence of global changes on the symbiosis. The third section dis­ cusses the influences of mycorrhizal fungi on biodiversity and ecosystem functioning. It also discusses factors that influence the diversity and structure of mycorrhizal fungal communities. The fourth section shows the multi­ trophic nature of the mycorrhizal symbiosis.