This chapter has highlighted the applications of chitosan nanoparticles in various fields such as; water, food and agriculture. Polyacrylamide-grafted CSNPs have been reported for the removal of (Cu) from water. Chitosan-alginate nanoparticles (CANPs) have been reported for the removal of Hg from industrial waste water. The Biomass of Cu and Co-doped alginate-coated CSNPs have been used for the removal of heavy metals. The chitosan nanoparticles have also been used in the food industry for various applications particularly in food packaging. In this connection, novel nano-fibrillated cellulose/chitosan nanoparticles for food packaging have also been reported. Synthesized fish gelatin/CSNPs composite films for food packaging have also been reported. Catechins and catechins-Zn complex loaded β-CSNPs for food products are also proved a good packaging material. In case of agriculture, chitosan-based polymers and nanoparticles have been used for fruits and seeds coating. The diverse range of applications for chitosan in agricultural commodities has primarily focused on the development of films and coatings because chitosan-based films have a high potential to extend shelf life. These polymers also have the potential to reduce the use of possibly dangerous farming methods and large quantities of toxic fertilizers while increasing the output of many agricultural plants. The evaluated polymers based on chitosan have delivered the greatest outcomes. The role of nano-delivery systems for agriculture has also been reported in detail. This chapter has provided another aspect of efficiency of chitosan nanoparticles by developing nano-delivery systems for agriculture. It has been evaluated that green nanotechnology and sustainable nanoparticles are being used in modern agriculture to apply precision farming, which seeks to increase output responsibly with few resources.