An exponentially growing number of nanotechnology-based products are providing new platforms for research in different scientific disciplines (e.g., life sciences and medicine). Biocompatible nanoparticles are expected to significantly impact the development of new approaches in medical diagnoses and drug delivery; however, very little is known about the effects of long-term exposure of different nanoparticles in different cell types and tissues. The first objective of this chapter is to provide a brief account of the current status of fluorescent nanoparticles (i.e., quantum dots, fluorescently-labeled micelles, and FloDots) that serve as tools for bioimaging and therapeutics. The second objective of this chapter is to describe the modes and mechanisms of nanoparticle-cell interactions and the "potential" toxic consequences thereof.