  Reactor neutrinos have been an important tool for both discovery and
precision measurement in the history of neutrino studies. Since the first
generation of reactor neutrino experiments in the 1950s, the detector
technology has been greatly advanced. New ideas, new knowledge, and modern
software also enhanced the power of the experiments. The current reactor
neutrino experiments, Daya Bay, Double Chooz, and RENO have led neutrino
physics into the precision era. In this article, we will review these
developments and accumulations, address the key issues in designing a
state-of-art reactor neutrino experiment, and explain how the challenging
requirements of determining the neutrino mass hierarchy with the next
generation experiment JUNO could be realized in the near future.
