In the present paper, we address a review of group-III nitride quantum wells and quantum dots realized by molecular beam epitaxy (MBE) using ammonia as a nitrogen source. Some important features of the growth of nitrides by MBE using ammonia are pointed out. We also emphasize the role of in situ analysis tools such as reflection high-energy electron diffraction. The optical properties of several kinds of quantum heterostructure are presented. They illustrate well the combined effects of polarization fields and carrier localization. Finally, the use of InGaN/GaN QWs in LEDs for white light emission is presented.