In vitro cultivation of arbuscular mycorrhizal (AM) fungi offers unique advantages in the investigation of these obligate biotroph micro-oganisms. Non-destructive microscopic observations, reliable cell physiology studies, clean biochemical and molecular analyses, highly controlled interactions studies with other microorganisms and mass production, are amongst the applications made possible by this technique. In vitro cultivation of AM fungi can be achieved on root organs (i.e. excised or transformed roots), but also on autotrophic plants, which opens new research and application opportunities. Large scale industrial production of biologically clean AM inocula produced in vitro has also become a reality.