The automotive sector is undergoing a shift towards decarbonization, with a particular focus on alternative solutions to traditional internal combustion engines (ICEs). While battery electric vehicles (BEVs) have gained popularity due to zero tailpipe emissions, they still face challenges such as limited range and infrastructure development. In this context, the resurgence of interest in hydrogen internal combustion engines (H2ICE) offers a promising pathway to carbon-neutral transportation. By utilizing gaseous hydrogen as fuel, H2ICE vehicles can achieve nearly zero emissions while benefiting from existing engine architecture. However, the adoption of H2ICE vehicles presents significant challenges, particularly in terms of hydrogen storage requirements and energy density. The IDTechEx report delves into the technical complexities of hydrogen engine combustion processes, emphasizing the importance of addressing nitrogen oxide (NOx) emissions and exploring exhaust gas treatment options. Additionally, the report evaluates market forecasts for H2ICE vehicles in sectors like passenger cars, aviation, and goods transportation, highlighting the unique hurdles each sector faces in decarbonization. Despite the obstacles, the industry remains optimistic about the potential of H2ICE as a viable alternative to traditional ICEs. The report underscores the need for further advancements in hydrogen storage technologies and infrastructure to enable the widespread integration of H2ICE vehicles across different sectors. By offering a detailed analysis of the current landscape and future prospects for hydrogen internal combustion engines, the report provides valuable insights into the role of H2ICE in the ongoing efforts to decarbonize transportation.