The potential role of mycorrhizal fungi biocontrol agent for the controlof fungal and nematode plant diseases has recently attracted considerableattention. Vesicular arbuscular-mycorrhizal infections generally inhibit orsometimes increase and occasionally have no effect on disease caused byfungal pathogens. The damage due to nematode diseases has also gener-ally decreased in mycorrhizal plants. Establishment of vesicular arbuscularmycorrhizae (VAM) in plants generally confers resistance to nematode para-sitism or adversely affects nematode reproduction. Although the improve-ment of plant nutrition, compensation for pathogen damage, and competitionfor photosynthates or infection sites have been claimed to play a protectiverole in VAM symbiosis. Information is scare, fragmentary, or even contro-versial, particularly concerning other mechanisms such as anatomical ormorphological and biochemical VAM induced changes in the root system,microbial change in the rhizosphere populations of mycorrhizal plants, andlocal elicitation of plant defense mechanisms by VAM fungi. In the presentchapter, interactions between VAM and phytopathogens (fungi and nema-tode) reported during past 2 decades are reviewed.