Arbuscular mycorrhizal fungi (AMF) are obligate symbionts that establish mutualistic associations with vascular plants, playing a critical role in nutrient exchange, soil structure, and plant health. This chapter explores the main structures of AMF, including intraradical and extraradical hyphae, arbuscules, vesicles, auxiliary cells, and spores, highlighting their formation, morphology, and function. The development of the symbiosis is divided into three phases: asymbiotic, presymbiotic, and symbiotic, each influenced by soil properties, host plant factors, and molecular signaling. The chapter also examines how abiotic and biotic factors regulate AMF life cycle stages, from spore germination to root colonization and nutrient exchange. Understanding these dynamics is fundamental to advancing the application of AMF in sustainable agriculture and soil restoration strategies.