Quantum dots (QDs) are nanoparticles with unique physical and chemical properties. QDs seem to show the greatest promise as biosensing, in vivo imaging techniques, nanomedicine, drug delivery, molecular pathology, and photovoltaics. Thus, the study of the QDs is one of the newest rapidly growing eras in modern chemistry. Such materials might have potential risks to human health, but still, the use of these materials is growing quickly. Specifically, the matter of QDs’ toxicity is very important, which is one of the major barriers in the growing world. This chapter describes the protocols related to the preparation of QDs, characterization techniques, their properties and applications and special consideration on the toxicology as well as surface modification of CdTeQDs.