© 2020 Elsevier LtdArbuscular mycorrhizal fungi (AMF) are plant root symbionts that continuously carry thousands of nuclei in their spores and hyphae. This unique cellular biology raises fundamental questions regarding their nuclear dynamics. This review aims to address these by synthesizing current knowledge of nuclear content and behavior in these ubiquitous soil fungi. Overall, we find that that nuclear counts, as well as the nuclei shape and organization, vary drastically both within and among species in this group. By comparing these features with those of other fungi, we highlight unique aspects of the AMF nuclear biology that require further attention. The potential implications of the observed nuclear variability for the biology and evolution of these widespread plant symbionts are discussed.