Melting temperature is one of the fundamental properties of materials. In principle, the melting temperature of a bulk material is not dependent on its size. However, as the size of a material decreases toward the nanometer size and approaches atomic scale, the melting temperature scales with the material dimensions. The melting temperature of a nanomaterial such as nanoparticles (isotropic) and nanorods/nanowires (anisotropic) is related to other fundamental physical properties for nanomaterial applications, including catalysts, thermal management materials, electronics materials, and energy materials.This book chapter focuses on both the theoretical and experimental studies of metallic nanoparticle melting temperature depression. Thermodynamic modeling and molecular dynamic (MD) simulations are discussed regarding the melting behavior of different nanostructures, such as spherical nanoparticles and nanowires. The currently available measurement techniques by using classical differential scanning calorimetry (DSC), recently developed nanocalorimeters, transmission electron microscope (TEM), and optical methods are introduced. In addition, the applications of metal nanoparticles with lower melting temperatures are discussed, such as nanosoldering and sintering for electronics assembly and packaging.