Globally, the race towards Net-Zero emissions has started. The country focuses on eliminating carbon dioxide and carbon monoxide emissions from the atmosphere. Currently, the dominating energy source is fossil-based, but the Net Zero vision warrants using an energy source that doesn’t contain carbon in its molecule. The transport sector is under stress as regulatory bodies put immense pressure on lowering tail-pipe emissions. Also, the power industries are looking for a fuel that uses non-carbonaceous radicals for combustion. Ammonia is the future fuel for decarbonizing the transport and power sectors. Also, low-carbon combustion technologies are needed to meet Net-Zero targets. The engine manufacturers are looking to retrofit the existing internal combustion engines to enable Ammonia combustion. The high auto-ignition temperature and slower chemical kinetics cause difficulty in initiating the ammonia combustion. Thus, the ignition or combustion improver is needed to begin the combustion. Although ammonia use in the transport and power sector is nascent, scientists are working on overcoming the challenges. This book covers the current challenges and state-of-the-art reviews of ammonia-fueled internal combustion engines, critical equipment and system-based risk factors of an ammonia-fueled, safety aspects of ammonia utilization, pre-chamber ignition system for lean combustion in a spark ignition engine, and recent optical techniques for soot characterization in fuel spray flames.