The increasing demand for agricultural productivity has intensified the use of conventional fertilizers, while inefficient nutrient utilization can contribute to nutrient losses and environmental degradation. Nano-fertilizers have emerged as a chemistry-driven approach for improving the delivery and utilization of essential plant nutrients. Their distinctive physicochemical properties, including high surface-area-to-volume ratios, tunable surface chemistry, and possibilities for controlled nutrient release, provide opportunities to redesign conventional fertilizer systems. This paper reviews the chemical principles underlying nano-fertilizers, their major classes, nutrient-release mechanisms, application approaches, and potential contributions to sustainable agriculture. Particular attention is given to nano-formulations containing nitrogen, phosphorus, potassium, zinc, iron, and other micronutrients, together with polymeric, mineral, carbon-based, and composite delivery systems. The discussion also considers the interaction of nanomaterials with soil components, roots, microorganisms, and the rhizosphere. Although the literature indicates considerable potential for improving nutrient-use efficiency and reducing nutrient losses, nano-fertilizers should not automatically be regarded as environmentally harmless alternatives. Their behavior depends on particle composition, size, surface properties, concentration, soil chemistry, environmental conditions, and transformation processes. Long-term ecological effects, production costs, standardization, regulatory requirements, and field-scale validation remain important challenges. A chemistry-based understanding of these factors is essential for developing nano-fertilizer systems that are effective, economical, and environmentally responsible.