Nanotoxicology is the study of the toxicity of nanomaterials. It is a branch of bionanoscience which deals with the study and application of toxicity of nanomaterials. Nanotoxicology is a sub-specialty of particle toxicology. It was proposed to address the adverse effects likely to be caused by nanomaterials that seem to possess toxicity effects that are unusual and not seen with larger particles. Nanotechnology is a double-edge sword, the same novel properties making nanoparticles attractive, makes them potentially toxic. Given the excitement associated with all of the nanotechnology applications, evaluating the potential hazards related to exposures to nanoscale materials and its products has become an emerging area in toxicology and health risk assessment. Typical nanoparticles that have been studied are titanium dioxide, alumina, zinc oxide, carbon black, and carbon nanotubes, and "nano-C60". Due to quantum size effects and large surface area to volume ratio, nanomaterials are highly reactive which potentially lead to toxicity as a result of their interactions with biological systems and the environment. Some nanoparticles seem to be able to translocate from their site of deposition to distant sites such as the blood and the brain. This has resulted in a sea-change in how particle toxicology is viewed- instead of being confined to the lungs; nanoparticle toxicologists study the brain, blood, liver, skin and gut. Nanotoxicology has revolutionised particle toxicology and rejuvenated it. The purpose of developing the concept of nanotoxicity is to acknowledge and evaluate the hazards and risks of Nanomaterials and measure safety. This discipline will be the important contribution for the development of a sustainable and safe Nanotechnology. Nanotoxicology is an interdisciplinary approach involving Toxicology, materials science, medicine, molecular biology etc.