Ultrasonic assisted EDM is a hybrid process that combines the physical phenomena of ultrasonic vibration with the EDM and/or micro-EDM process to improve the process stability and performance. The ultrasonic vibration was found to be applied effectively in both workpiece and tool electrode based on the applications and structures to be machined. This review paper provides an overview of the principle of EDM and ultrasonic vibration assisted EDM, as well as includes a comprehensive review of various aspects of ultrasonic vibration assisted EDM including major challenges and guidelines to resolve the challenges in the future research. It can be concluded from the literature that ultrasonic vibration assistance increases the MRR, surface roughness and tool wear ratio due to the reduced arcing, inactive pulses, cavitation effect and stable discharge. The MRR can be enhanced by increasing voltage, current and vibration amplitude. Increase of discharge voltage, current, pulse duration and ultrasonic vibration amplitude causes increased surface roughness, whereas higher frequency vibration results in a lower surface roughness due to the generation of multiple channel of discharge. On the other hand, TWR can be reduced by increased vibration amplitude, tool rotation and planetary affect. The ultrasonic vibration assisted EDM was found to be especially effective, where the flushing of debris becomes challenging, such as in deep micro-holes. The aspect ratio and inside surface quality of the micro-holes could be significantly improved by applying ultrasonic vibration in micro-EDM drilling of deep micro-holes. Ultrasonic vibration assisted EDM was also found to be effective during the machining of complex blind structures for multi-scale die and mould making. The ultrasonic vibration assisted EDM was also found to improve the surface integrity by reduction of the ineffective pulses, that is, arching and short-circuiting, on the surface, thus reducing the thickness of recast layer and residual stress. Finally, it can be concluded that ultrasonic vibration assisted EDM is an effective process to machine difficult-to-cut materials and complex multi-scale structures on a range of materials including metals and ceramics, thus, improving the process capability of the traditional EDM and micro-EDM process.