Heat transfer at nanoscales differs significantly from that in macroscales because of size effects on the phonon and electron transport. Nanoscale heat transfer effects have significant implications for the microelectronic and microphotonic industries, from the thermal management, the device design and reliability, and the active cooling considerations. Past studies have shown that heat conduction in nanostructures can be significantly impeded below that of the predictions of the Fourier theory. Such size effects imply higher device temperatures than anticipated and demands more stringent thermal management measures. On the other hand, same size effects can be exploited for developing highly efficient thermoelectric (TE) materials for direct cooling. This paper starts with a discussion on some nanoscale heat transfer effects and their impacts on the device performance, particularly using thermal conductivity reduction in superlattices as an example, followed by a review of recent developments in nanostructured TE materials