At least six steps involving recognition, signaling, or communication between host root and arbuscular mycorrhizal (AM) fungi appear to be necessary for the fungus to complete its life cycle. Recent developments in in vitro culture technology, including the use of germinated aseptic fungal spores, roots grown in liquid culture, dual culture of a host root and single spore on a solid support medium, and the split plate technology, have provided the means to study specific steps in detail. Although in vitro culture is greatly simplified over the root-soil environment, it has provided a way to study early recognition events between a single germinated fungal spore and a specific host root without complication from other rhizosphere components.