Micro-EDM (electro-discharge machining) is a derived form of EDM process especially evolved for micro-machining. The machining and removal of nonconducting materials are performed in EDM by providing an auxiliary conductive layer (assisting electrode), which is recreated after every spark discharge. Hence, an assisting conductive layer is formed on the workpiece surface to begin the spark erosion process. A robust model deducing the spark gap in a single discharge in μ-EDM needs to be designed to evaluate various phenomena in the pre-breakdown period. It is to be understood that the gap phenomenon in EDM involves various variables and is highly complicated. Numerous improved simulations have been performed to further discover and contribute towards modifications in EDM technology. Recent work provides new insights and challenges based on existing theories on the interelectrode gap as well as the spark discharge associated with the EDM phenomenon. © 2021 Elsevier Ltd. All rights reserved.