  Neutrinos exhibit an interesting phenomenon called 'neutrino oscillation', in
which a neutrino changes its flavor after traveling some flight length. Many
experiments measured the mixing angles and mass differences, but the angle
$\theta_{13}$ had been unmeasured due to its smallness compared to others.
During 2011 and 2012, series of new-generation neutrino experiments reported
positive results in $\theta_{13}$ search, and its value has been determined to
be just below the previous upper limit. The non-zero result of $\theta_{13}$ is
a very good news for future of neutrino physics, since it opens a possibility
of measuring the CP violation phase in the lepton sector. An introduction to
neutrino oscillation and latest experimental results are presented. A detail is
put on Double Chooz reactor experiment, in which the author is involved.
