  I discuss some theoretical aspects of how to observe leptonic CP violation.
It is divided into two parts, one for CP violation due to Majorana, and the
other more conventional leptonic Kobayashi-Maskawa (KM) phases. In the first
part, I estimate the effect of Majorana phase to observable of neutrinoless
double beta decay experiments by paying a careful attention to the definition
of the atmospheric scale Delta m^2. In the second part, I discuss
Tokai-to-Kamioka-Korea two detector complex which receives neutrino superbeam
from J-PARC as a concrete setting for discovering CP violation due to the KM
phase, as well as resolving mass hierarchy and the theta_{23} octant
degeneracy. A cautionary remark is also given on comparison between various
projects aiming at exploring CP violation and the mass hierarchy.
