Fungal pathogens cause significant yield losses in global agriculture, with species such as Magnaporthe oryzae, Fusarium spp., and Botrytis cinerea posing major threats. Although effective, conventional chemical fungicides can lead to the development of resistance, environmental contamination, and health risks. Chitosan nanoparticles (CNPs), derived from the deacetylation of chitin, offer an eco-friendly and biodegradable alternative for managing fungal diseases. Their nanoscale size, positive surface charge, and functional versatility enable them to directly combat fungi through cell wall disruption, changes in membrane permeability, induction of reactive oxygen species, inhibition of spore germination, and activation of the host plant immune system. CNPs also act as carriers for antifungal agents, facilitating controlled release and targeted action. They are applied as foliar sprays, soil and seed treatments, and postharvest coatings, with proven effectiveness in greenhouse and field trials. Studies comparing CNPs with traditional fungicides and other nanomaterials highlight their advantages, especially in resistance management and reducing chemical use. This chapter aims to explore the potential of chitosan nanoparticles in controlling fungal plant diseases, highlighting their mechanisms of action, applications, benefits, and limitations in sustainable crop protection. However, challenges such as scale-up, cost, stability, phytotoxicity, and regulatory issues remain. Combining CNPs technology with precision agriculture, smart delivery systems, and multifunctional nanocomposites can further enhance their role in sustainable crop protection.