Wireless sensor and actor networks (WSANs) have promising applications in a large number of fields, recently including the smart grid among many others. Smart grid is the future electricity grid that adopts two-way communications and energy flow between the operators and the consumers for the betterment of electrical services. Efficient energy use is among the fundamental goals of the smart grid. 124Hence, utilizing WSANs for smart energy use has been a significant research topic recently. In this chapter, we will summarize the research on WSAN-based energy management in the smart grid. In the smart grid, WSANs can be used to monitor and control power consumption of the consumers. WSAN-based residential energy management schemes can schedule appliances such that the use of electricity from the grid during peak hours is reduced, which consequently reduces the need for the power from the peaker plants and reduces the carbon footprint of the household. Moreover, it is possible to use locally generated power according to time of day and sell the excess energy to the grid. For instance, consumers may monitor their appliances while they are away from home; in addition, they can select from which resource to supply electricity to their appliances. Thus, consumers need energy and demand management tools to make decisions to reduce their costs and at the same time to reduce their contribution to peak load. In this chapter, we will first give an overview of the application areas of WSANs in the power grid including generation, transmission and distribution, and consumer segments. We will then discuss the incentives for smart energy use, followed by available communication technologies for WSANs such as Zigbee, low-power Wi-Fi, Z-wave, and Wavenis, and compare their applicability in smart energy use applications. We will further summarize the WSAN-based smart energy use tools in the literature. Finally, we will conclude our chapter by discussing the challenges and outlining the open issues.