The effects of mycorrhizal fungi have traditionally been considered within the rather narrow perspective of their effects on the mineral nutrition of individual plants. Most biologists are familiar with the idea that these symbiotic fungi may improve plant uptake of dissolved mineral nutrients. What other effects do these symbionts have? Research during the past 20 years has increasingly viewed symbiotic mycorrhizal associations between plants and fungi within a wider, multifunctional perspective. New molecular methods have been applied to investigate mycorrhizal fungal communities (Bruns & Bidartondo, 2002) and greater attention has been paid to their possible effects at the level of the plant community. As we have acquired greater knowledge about fungal species diversity, so we have become more aware of the potential functional diversity of mycorrhizal fungi. The new multifunctional perspective includes mobilisation of N and P from organic polymers, possible release of nutrients from mineral particles or rock surfaces via weathering, effects on carbon cycling, interactions with myco-heterotrophic plants, mediation of plant responses to stress factors such as drought, soil acidification, toxic metals and plant pathogens, as well as a range of possible interactions with groups of other soil microorganisms.