The recent design and development of nanosized particulate materials, generally termed as nanomaterials, and their growing employment in several fields spanning from electronics to medicine, created an immediate need for approaches to assess nanomaterial safety. Owing to their distinctive physicochemical and kinetic characteristics, their behavior toward biological systems is influenced by many factors including shape, coatings, solubility, and aggregation of the particles, but is also dictated by the living entity exposed to the nanoparticle, making the prediction of toxicity a great challenge. Owing to the variety of the nanoparticles and systems employed to assess their toxicity, many diverse mechanisms have been identified that contribute to their adverse effects on cells, tissues, and organs of living organisms, and the relevant literature is exponentially growing. Many studies have reviewed in this fast changing research area, addressing several aspects spanning from nanoparticle physicochemical properties that influence toxicity to the impact on environment and human health. Here we focus on the possible molecular events elicited in distinct subcellular compartments by nanomaterials, whose potential hazardous nature is here considered by calling them "nanostressors." We provide an overview of various NP evoked molecular processes generally assembled under the common term nanotoxicology, pointing out the most advanced technological tools (microarray, RNAseq) and underexplored effect (epigenetic) recently employed in the nanotoxicology field. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved