Conventional chemical fertilizers and pesticides are used with poor efficiency: 40–70% of applied nitrogen, 80–90% of phosphorus, and 50–70% of potassium are lost to volatilization, leaching, and fixation, while more than 90% of sprayed pesticides fail to reach their target organism. These losses drive nutrient runoff, soil degradation, pesticide resistance, and biodiversity loss. Nanotechnology offers an alternative: nano-fertilizers and nano-pesticides (1–100 nm) that deliver active ingredients in a controlled, targeted, and often stimuli-responsive manner. This review synthesizes current evidence on the synthesis, classification, and plant-uptake mechanisms of nano-agrochemicals; evaluates their efficacy relative to conventional formulations; and critically examines the phytotoxicity, soil-microbiome, and regulatory concerns that currently constrain commercial adoption. We conclude that while nano-agrochemicals offer measurable gains in nutrient-use efficiency and pest-control precision, their large-scale deployment requires standardized biosafety testing and harmonized regulation before they can be considered a mature substitute for conventional inputs.