Abstract:  Neutrino flavor oscillation implies that neutrinos have mass and they mix with each other, providing an evidence for physics beyond the Standard Model.  The most recent development in this field is the discovery of the smallest lepton mixing angle theta13.  This signifies an important breakthrough in validating the standard three-flavor oscillation picture of neutrinos.  First, I will briefly discuss the three-flavor neutrino oscillation, and identify the fundamental oscillation parameters which govern this phenomenon.  Then, I will review the present knowledge about these parameters, and list the remaining fundamental issues which need to be addressed in current and future neutrino oscillation experiments.  Next, I will elucidate the role of currently running and future long-baseline experiments in resolving these unsolved issues.  I will also mention about the upcoming India-based Neutrino Observatory (INO) facility whose aim is to explore the Earth's matter effect by observing the energy and zenith angle dependence of the atmospheric neutrinos in the multi-GeV range.  Finally, I will describe how this experiment is going to play an important role to address some of the outstanding issues in neutrino oscillation physics.