Heat transfer in nanostructures differ significantly from that in the bulk materials since the characteristic length scales associated with heat carriers, i.e., the mean free path and the wavelength, are comparable to the characteristic length of the nanostructures. Nanostructure materials hold the promise of novel phenomena,properties, and functions in the areas of thermal management and energy conversion. Three important topics are studied with respect to energy transport in nanostructure materials for micro/nano electronic and thermoelectric applications: 1) the role of nanocomposites in improving the thermal efficiency of thermoelectric devices, 2) the interfacial thermal resistance for the semiconductor/metal contacts in thermoelectric devices and for metallic interconnects in micro/nano electronic devices, 3) the interaction between the energy carriers namely electrons/carriers with phonons which lead to a significant non-equilibrium at the semiconductor-metal contacts.