The growing global population demands the adoption of sustainable agricultural practices. Metal-based nanoparticles (Ag, Cu, ZnO, TiO₂, Fe₂O₃, Au, Ca, and Mg) present promising tools for addressing biotic and abiotic stresses, enhancing nutrient efficiency, and reducing environmental impact. This review aims to provide a systematic synthesis of their agricultural applications, organized according to their distinct functions: antifungal, insecticidal, antibacterial, and nematicidal agents, biostimulants and photostimulators that enhance photosynthesis, as well as biosensors for pathogen and toxin detection. Emphasis is placed on «green» synthesis routes utilizing plant extracts and microorganisms. A dose-dependent response is consistently observed across studies: low to moderate nanoparticle concentrations promote growth and stress tolerance, whereas high concentrations induce toxicity. Despite their efficacy, significant safety concerns remain, particularly regarding adverse effects on beneficial organisms, including pollinators and non-target nematodes, as well as broader environmental risks. Key research gaps include the development of species-specific, non-toxic formulations and the need for comprehensive studies on the impact of nanoparticles on healthy plants and soil microbial communities, which are critical for ensuring the safe and sustainable integration of nano-agrochemicals into agricultural systems.