Quantum dots (QDs) have shown promising potential to many biomedical and biological applications, mainly in drug delivery or activation and cellular imaging. These semiconductor nanoparticles, QDs, whose particle size is in the range of 2-10 nanometer with unique photo-chemical and -physical properties that are not possessed by any other isolated molecules, have become one of the distinct class of imaging probes and worldwide platforms for manufacturing of multifunctional nanodevices. In this chapter, properties, applications of QDs, and importance in the biomedical field especially in drug delivery is presented.