Arbuscular mycorrhizal fungi (AMF) have played a fundamental role in plant evolution, forming symbiotic associations for over 460 million years. Fossil and molecular evidence suggests that AMF predate the earliest land plants, influencing their adaptation and nutrient acquisition. The evolutionary trajectory of AMF is characterized by significant morphological and phylogenetic changes, including the transition from their ancestral traits to the diversity observed today. Despite extensive research, uncertainties remain regarding their phylogenetic relationships within the fungal kingdom. Early AMF taxonomy was primarily based on morphological characteristics, leading to the classification of several genera and species. However, the advent of molecular techniques revolutionized AMF systematics, refining phylogenetic groupings and revealing cryptic diversity. This chapter traces the history of AMF taxonomy through seven major phases, from initial classifications in the nineteenth century to modern molecular-based approaches. Key milestones include the recognition of the Glomeromycota phylum, the introduction of molecular markers, and the continuous reassessment of genera and species. While molecular advances have improved classification, challenges persist in defining species boundaries and integrating morphological and genetic data. This chapter highlights the importance of AMF in plant evolution and ecosystem functioning, emphasizing the need for further research to resolve phylogenetic uncertainties and enhance classification systems.