In recent decades, power line communication (PLC) has attracted considerable attention from the research community and industry, as well as from regulatory and standardization bodies. In this paper, we provide an overview of both narrowband and broadband systems, covering potential applications, regulatory and standardization efforts, and recent research advancements in channel characterization, physical layer performance, medium access, and higher layer specifications and evaluations. We also identify the areas of current and further study that will enable the continued success of PLC technology.