Atmospheric neutrinos are produced by cosmic ray interactions with the air nuclei in the atmosphere. The interactions of these neutrinos have been observed in underground detectors for about 50 years. In 1998, neutrino oscillations were discovered by the detailed studies of these neutrinos with the Super-Kamiokande experiment, a water Cherenkov detector with the total mass of 50 kilo-tons. In this lecture, I will discuss the experimental studies that led to the discovery of neutrino oscillations, the present studies, and the possible future neutrino experiments for further studies of neutrino properties. The implications of the small neutrino masses will also be discussed briefly.