Semiconductor nanocrystals with sizes in the quantum confinement regime (2-10 nm) present special physical and chemical properties. Additionally, environment-friendly quantum dots (QDs), as zinc oxide and zinc sulfide, offer many practical usages. Herein the ZnO semiconductor nanocrystals properties will be preferentially explored, such as its luminescence, broad spectrum UV absorber and electronics performances, and therefore its multifunctionality, as well as its advantages compared to some toxics QDs. A review is carefully presented stressing some synthesis approaches for applications reasons toward devices, chemosensors, biological labels, UV-absorbers and photocatalysis. ZnO QDs have been used in combination with organic and other inorganic materials. Hybrid materials have many advantages compared to their individual contents leading to important contributions to science and technology. As a result, an important growth in material fields is noticeable.