We have used low energy electron-excited nano-luminescence (LEEN) spectroscopy to obtain electronic band gap, confined state, and deep level trap information from GaN surfaces and buried interfaces on a nanometer scale. This local spectroscopy provides information available only indirectly by other electronic techniques. Using LEEN in combination with other surface science methods, we have probed the localized electronic states at GaN free surfaces, metal-CaN contacts, GaN/InGaN quantum wells, AlGaN/GaN pseudomorphic heterostructures. and GaN/sapphire template layers, Their properties are sensitive to the interface chemical composition, bonding, and atomic structure and in turn to the specifics of the epitaxial growth. The results highlight new methods for understanding and controlling electronic properties of GaN interfaces and their future applications,