Neutrinos are elementary particles in the Standard Model. Neutrino oscillation is a quantum mechanical phenomenon beyond the Standard Model. Neutrino oscillation can be described by two independent mass-squared differences Delta m (21) (2) , Delta m (31) (2) (or Delta m (32) (2) ) and a 3 x 3 unitary matrix, containing three mixing angles theta (12), theta (23), theta (13), and one charge-parity (CP) phase. theta (12) is about 34A degrees and determined by solar neutrino experiments and the reactor neutrino experiment KamLAND. theta (23) is about 45A degrees and determined by atmospheric neutrino experiments and accelerator neutrino experiments. theta (13) can be measured by either accelerator or reactor neutrino experiments. On Mar. 8, 2012, the Daya Bay Reactor Neutrino Experiment reported the first observation of non-zero theta (13) with 5.2 standard deviations. In June, with 2.5x previous data, Daya Bay improved the measurement of sin(2)2 theta (13) = 0.089 +/- 0.010(stat) +/- 0.005(syst).