Arbuscular mycorrhizal symbioses occur between fungi and the majority of plant species. They are important for plant nutrition, plant growth, protection from pathogens, plant diversity, nutrient cycling, and ecosystem processes. A key goal in research is to understand the molecular basis of the establishment, regulation, and functioning of the symbiosis. However, lack of knowledge on the genetics of the fungal side of this association has hindered progress. Here, we show how several key, recently discovered processes concerning the genetics of arbuscular mycorrhizal fungi could be essential for ultimately understanding the molecular genetics of this important symbiosis with plants.