Gallium nitride (GaN), a member of the family of III-V semiconductor compounds, has been investigated intensively and have found extensive applications. Recent development has suggested that GaN may be used as an excellent host material for light-emitting devices (LEDs) that operate in the blue and ultraviolet region, due to its wide and direct band gap. Nano-materials often present novel properties that are different from the corresponding bulk materials due to their unique structures, high specific surface area and quantum confinement effects. This book discusses several topics on the structure, thermal properties and applications of GaN. Some of these topics include the effects of radiation damage in GaN and and related materials; low-dimensional GaN; structural and dielectric properties of the GaN and silica nanoparticles investigated by molecular dynamics; and GaN bulk and nanostructures for spintronic application.