Abstract: Electrostatic spraying can be expected to integrate with unmanned aerial vehicle (UAV) platforms in modern agriculture. The plant protection can also represent an innovative electrostatic spraying. The promising potential can be offered to improve the utilization efficiency and deposition uniformity of pesticides in precision agriculture. Among them, the high-voltage electric fields can be applied to the electrostatic spraying. The droplets can be induced to carry the electrical charges, thereby modifying their trajectory for the high adhesion to the plant surfaces. Particularly, it is beneficial to the full coverage of the abaxial (underside) surfaces of leaves, which are typically difficult to reach under conventional spraying. This review aims to examine the history, theory, and current research in electrostatic spraying for crop protection UAVs. Three mainstream charging mechanisms were systematically outlined—corona, inductive, and contact charging, with emphasis on their physical principles, advantages, limitations, and the voltage ranges applicable to each. The inductive charging dominated the current applications, due to its relative safety and engineering simplicity. In addition, the structural designs of electrostatic spraying were also considered, including the electrode configurations (ring-type, cone-type, and embedded parallel plates), the selection of electrode materials (e.g., copper, nickel, stainless steel), and the integration of air-assisted mechanisms. The air assistance was crucial to support the penetration and distribution of the droplets, particularly under the high-speed rotor-induced turbulence during UAV operations. Furthermore, the key evaluation techniques were surveyed, such as the charge-to-mass ratio (CMR) measurements, droplet size characterization (e.g., VMD), and deposition detection. It was still lacking in the standardized testing protocols. There was a great discrepancy between laboratory measurements and field performance, especially under complex outdoor conditions with the wind, temperature, and humidity. The electrostatic spraying was also analyzed using the droplet trajectory. Three interactions were also dominated in the electrostatic field: 1) the induced fields between droplets and plant targets, 2) repulsive fields among charged droplets, and 3) externally applied fields between the nozzle and target. Each mechanism contributed differently to the droplet motion, distribution, and deposition efficiency. Nevertheless, there were multiple challenges on the electrostatic UAV spraying, despite its theoretical advantages. These included: the limited understanding of the charge decay during droplet transport, insufficient high-voltage insulation in the compact UAV systems, and lack of the specialized nozzles to produce the uniformly fine droplets that responded well to electric fields. Moreover, the effectiveness varied significantly across the crop types, due to the differences in the leaf surface conductivity and canopy architecture. A set of recommendations were given for the future research. 1) The high-voltage contact and corona charging can be advanced with improved safety features. 2) The electrostatically-optimized nozzles and adjuvants can be developed in the future. 3) The evaluation metrics were refined to integrate the CMR with the droplet size distribution. 4) It is also required to conduct large-scale, and crop-specific field validations. Electrostatic UAV spraying can be expected to serve as the precision pesticide application, with the UAV technologies, high-voltage electronics, system miniaturization, and environmental adaptability. This technology can also hold great promise to reduce pesticide application for environmental protection in sustainable agriculture.