Abstract: Arbuscular mycorrhizal (AM) symbiosis is the mutualistic association between AM fungi and most terrestrial plants: the plant roots offer carbohydrates to the fungi; in return, the fungi assist the plants with uptake of mineral nutrients, particularly phosphate, from soil, and their subsequent transfer to the root cortical cells. The formation of AM symbiosis involves complicated pathways of signal exchange and transduction, with stringent and coordinated programs. This mini-review focuses on the current knowledge in the signal transduction pathways in AM plants. Such pathways in higher plants are similar, in part, to nodulation signal pathways in legumes and are related to calcium signaling. Many detailed action models in AM signal transduction are not clear yet but may be revealed soon.