Smart grid aims at improving the efficiency, reliability, security, and quality of service (QoS) of the current electricity grid by exploiting the advances in communication and information technology. In parallel to size of the electricity grid, smart grid communication infrastructure should cover a very large geographical area that may extend from remote generation sites to densely populated residential regions and inside buildings, homes, and electricity-power-system environments. In such an extensive communication network, different communication technologies operating on different communication medium are likely to coexist. Among the communication technologies available, wireless and power line communication (PLC) based solutions are comparatively attractive especially considering cost of the initial investment required for the realization of a communication network with such an immense size. In this dissertation, a detailed investigation of wireless and PLC channel characteristics of the smart grid networks is presented. Among the topics discussed are the time variation characteristics of wireless channels, root-mean-squared (RMS) delay spread and path amplitude statistics of PLC channels, and the impact of impulsive noise on orthogonal frequency division multiplexing (OFDM) systems.