Abstract Direct Current (DC) fast charging enables the direct delivery of megawatt (MW) scale power to the large battery systems of heavy-duty electric vehicles (EVs), such as trucks, buses, and construction machinery. This contrasts with Alternating Current (AC) charging, which is constrained by the limited capacity of onboard chargers. The feasibility of ultra-fast DC charging has been driven by advancements in semiconductor technology offering higher voltage and current handling capabilities as well as improvements in battery energy density. Ongoing research indicates continued growth in both semiconductor power handling and battery storage capacity, further strengthening the case for ultra-fast DC charging. Key benefits include significantly higher charging efficiency, drastically reduced charging times, and lower driver fatigue. However, unlike AC systems, DC charging infrastructure presents unique protection challenges. These challenges arise from the rapid rise of DC fault currents (high di/dt), which is a consequence of the DC line's negligible inductive reactance due to the zero frequency of DC current, the absence of natural current zero-crossings, and the limited availability of effective DC protection devices. This paper provides a comprehensive review of existing protection technologies applicable to DC fast charging systems, identifies critical gaps in current approaches, and evaluates potential solutions for Low Voltage (LV, <1.5 kV) and Medium Voltage (MV, 1.5-35 kV) DC applications. Finally, it proposes a forward-looking roadmap for the development of protection technologies essential for the safe and reliable deployment of megawatt-scale DC fast charging infrastructure for heavy-duty transportation. Key words: Direct Current (DC), Megawatt (MW), Low Voltage (LV), Medium Voltage (MV)