Nanoscale particles are known to exhibit novel properties that make them different from their corresponding bulk-scale materials. Concerns have been raised that the very same properties that make them interesting might also have negative health effects, which cannot easily be derived from the known toxicity of the macroscopic material. Hence, major gaps in the knowledge necessary for assessing their risk to human health currently exist. There is also a lack of existing methodologies to improve techniques for nanoparticle characterization, their detection in biological systems, as well as the biological activity of such systems. The complexity of this problem is amplified by the huge variety of nanoscale materials and potential biomolecules and cells. This special issue mostly contains mini-reviews, which summarize the current and previous work of the contributing groups performing research in this field.