  The discovery of neutrino mixing and oscillations over the past decade
provides firm evidence for new physics beyond the Standard Model. Recently,
theta13 has been determined to be moderately large, quite close to its previous
upper bound. This represents a significant milestone in establishing the
three-flavor oscillation picture of neutrinos. It has opened up exciting
prospects for current and future long-baseline neutrino oscillation experiments
towards addressing the remaining fundamental questions, in particular the type
of the neutrino mass hierarchy and the possible presence of a CP-violating
phase. Another recent and crucial development is the indication of non-maximal
2-3 mixing angle, causing the octant ambiguity of theta23. In this paper, I
will review the phenomenology of long-baseline neutrino oscillations with a
special emphasis on sub-leading three-flavor effects, which will play a crucial
role in resolving these unknowns. First, I will give a brief description of
neutrino oscillation phenomenon. Then, I will discuss our present global
understanding of the neutrino mass-mixing parameters and will identify the
major unknowns in this sector. After that, I will present the physics reach of
current generation long-baseline experiments. Finally, I will conclude with a
discussion on the physics capabilities of accelerator-driven possible future
long-baseline precision oscillation facilities.
