Ammonia is emerging as a viable alternative to fossil fuels in combustion systems, helping reduce carbon emissions. However, its use faces challenges, including NOx emissions and low flame speed. This review explores current advancements in using ammonia as a fuel substitute, highlighting the complexities that various systems need to overcome before reaching full commercial maturity. The article incorporates insights from industrial partners working on green ammonia technologies and addresses fundamental complexities of ammonia combustion, crucial for its practical and industrial implementation. Ammonia can be produced from fossil fuels or renewable sources, offering advantages over hydrogen, such as lower storage and transportation costs, easier handling, and better commercial viability. It can be directly converted to electricity in turbines, engines, or fuel cells. However, ammonia-based energy systems face key challenges, including carbon-free synthesis, power generation at utility-scale, public policy and safety regulations, and competitive economics. Ammonia production accounts for 2% of total final energy consumption and 1.3% of CO2 emissions. The ammonia industry faces strong challenges for the 2050 net-zero emissions scenario, requiring emission reductions and increased sustainability. Ammonia is a great candidate to support the transition to a net-zero carbon economy, but combustion emission products remain a research focus. The review critically discusses ammonia combustion fundamentals, essential for its application in industrial facilities. Key barriers include high auto-ignition temperature, low flame speed, narrow flammability limits, high heat of vaporization, and high NOx emissions. The review also addresses the need for thorough economic studies to determine ammonia's viability as an energy system. Fig. 2 shows historical ammonia production data from 1945 to 2022 and future projections up to 2050.Ammonia is emerging as a viable alternative to fossil fuels in combustion systems, helping reduce carbon emissions. However, its use faces challenges, including NOx emissions and low flame speed. This review explores current advancements in using ammonia as a fuel substitute, highlighting the complexities that various systems need to overcome before reaching full commercial maturity. The article incorporates insights from industrial partners working on green ammonia technologies and addresses fundamental complexities of ammonia combustion, crucial for its practical and industrial implementation. Ammonia can be produced from fossil fuels or renewable sources, offering advantages over hydrogen, such as lower storage and transportation costs, easier handling, and better commercial viability. It can be directly converted to electricity in turbines, engines, or fuel cells. However, ammonia-based energy systems face key challenges, including carbon-free synthesis, power generation at utility-scale, public policy and safety regulations, and competitive economics. Ammonia production accounts for 2% of total final energy consumption and 1.3% of CO2 emissions. The ammonia industry faces strong challenges for the 2050 net-zero emissions scenario, requiring emission reductions and increased sustainability. Ammonia is a great candidate to support the transition to a net-zero carbon economy, but combustion emission products remain a research focus. The review critically discusses ammonia combustion fundamentals, essential for its application in industrial facilities. Key barriers include high auto-ignition temperature, low flame speed, narrow flammability limits, high heat of vaporization, and high NOx emissions. The review also addresses the need for thorough economic studies to determine ammonia's viability as an energy system. Fig. 2 shows historical ammonia production data from 1945 to 2022 and future projections up to 2050.