Nanoscience and nanotechnology have piqued the scientific imagination over the last two decades. The development of nanoparticles and nanofillers with specific and/or tailored properties, as well as their application in various fields, has been the primary focus of research in these fields. However, one critical aspect that has received little attention is the impact of nanoparticles on the environment and human health. This chapter discusses the different types, properties, applications, and physical and chemical properties of nanoparticles and nanofillers, which may have an impact on the environment and human health from a toxicological standpoint.