Global concern over the environmental impact of petroleum-based fuels has increased significantly in recent years, driven by the evidence of climate change, and dwindling fossil fuel reserves. Consequently, policymakers are exploring sustainable energy solutions to address these challenges. Although the transition to electrification has garnered significant attention across various economies, the complexity of global resource distribution, developing the required infrastructure, and realizing technological maturity suggest that a one-size-fits-all solution may not suffice in the long term. Hence, extensive research efforts are underway to identify sustainable and affordable alternatives that can use the existing infrastructure while requiring minimal changes in the hardware design. Among the several alternatives, hydrogen has emerged as one of the promising solutions, offering potential pathways to address environmental concerns and energy security. This chapter reviews the recent advancements and challenges associated with integrating hydrogen fuel in compression ignition engines. The advantages and disadvantages of using hydrogen as a fuel are discussed by analyzing its physical, chemical, and thermodynamic properties first. This is followed by outlining various combustion modes for operating hydrogen in spark-ignited and compression ignition engines. Their effects on combustion characteristics, engine, and emissions performance are presented, and the necessary modifications required to adapt existing engines to run efficiently on hydrogen are discussed. Finally, the applications of hydrogen with relevant recommendations for its adoption, considering the unique requirements and challenges, are evaluated.