Quantum dots (QDs) are nanocrystals of a semiconductor material that exist in a size regime less than 10 nm. QDs have become promising nanoparticles for a wide variety of different applications. However, the major drawback of QDs is their potential toxicity. This review reports on some recent methods for the synthesis of QDs and explores their properties, structures, applications, and toxicity. QDs are extraordinary because their minute size produces a physically confined electron cloud, an effect known as the quantum confinement. Certainly, because of their special properties as they had a great unique optical, electronic, and chemical properties that were not observe in other materials. These unique properties of the QD are an attractive material for a variety of scientific and commercial applications, most of them recently been realized, such as biosensors, bioimaging, photodetectors, displays, solar cells, wastewater treatment, and quantum computers. Finally, but not the end, an interesting potential QD application in future perspectives will expect as light-emitting diode products, biomedical applications, and Li-Fi.