Chitosan, a biopolymer derived from chitin, has garnered significant interest in sustainable agriculture for its dual function in direct pathogen control and the induction of plant defence mechanisms. Chitosan nanoparticles (CNPs) are a type of chitosan that has better physicochemical features, such as a larger surface area, a higher charge density and a higher bioactivity. This makes it easier for them to stick to plant surfaces, distribute bioactive substances to specific areas and last longer. CNPs can change the way plants send stress signals, make antioxidant enzymes work better and work with secondary metabolites to make crops more resistant to disease. Chitosan-based nano-formulations also work as multifunctional carriers for agrochemicals, micronutrients and elicitors, which fit with smart agriculture and integrated pest management (IPM) methods. However, widespread use is hard because of problems like standardizing synthesis, making it cost-effective, keeping the environment safe and following the rules. Interdisciplinary research and new technologies can help solve these problems and make CNPs a key part of crop protection systems that are both climate-resilient and resource-efficient.