Stringent energy constraint imposed by the small size of sensing nodes is a critical issue in realizing the perpetual operation of wireless sensor networks/ Internet of things (WSNs/IoTs). Unmanned aerial vehicle (UAV) network is a promising technology that is already being used for several applications. They can be a substantial and convenient source of energy harvesting for WSNs/IoT applications, especially in far-flung areas. However, due to their mobile nature, constraints like budget and airspace congestion, and different capabilities of different UAVs, multiple factors need to be considered in designing UAV-assisted energy harvesting schemes. In this chapter, we present a comprehensive review of various schemes that are proposed to improve energy harvesting directly or indirectly by improving some dependent performance objectives in UAV-assisted WSNs/IoT networks.