This paper discusses the potential of ammonia as a carbon-free fuel and recent advances in ammonia combustion technology and its underlying chemistry. Ammonia, which contains 17.8% hydrogen by mass, can be produced from renewable hydrogen and nitrogen from the air. Its thermal properties are similar to propane, making it an attractive hydrogen and energy carrier. Ammonia has been used for over a century as a fertilizer, chemical raw material, and refrigerant. While it can be used as a fuel, challenges include low flammability, high NOx emissions, and low radiation intensity. Overcoming these challenges requires further research into ammonia flame dynamics and chemistry. The paper discusses recent applications of ammonia fuel in gas turbines, co-fired with coal, and in industrial furnaces, implemented under Japan's "Cross-ministerial Strategic Innovation Promotion Program (SIP): Energy Carriers." It also covers fundamental aspects of ammonia combustion, including characteristics of laminar premixed flames, counterflow twin-flames, and turbulent premixed flames stabilized by a nozzle burner at high pressure. The paper discusses the chemistry of ammonia combustion related to NOx production, processes for reducing NOx, and validation of ammonia oxidation kinetics models. LES results for a gas-turbine-like swirl-burner are presented to develop low-NOx single-fuelled ammonia gas turbine combustors. The paper also discusses the chemical kinetics of ammonia oxidation and fuel NOx, including the extended Zeldovich mechanism in ammonia combustion. Ammonia combustion is a promising alternative to fossil fuels for reducing greenhouse gas emissions, but challenges such as low flammability and high NOx emissions need to be addressed. The paper highlights the importance of ammonia as a carbon-free fuel and the need for further research into its combustion characteristics and chemistry.This paper discusses the potential of ammonia as a carbon-free fuel and recent advances in ammonia combustion technology and its underlying chemistry. Ammonia, which contains 17.8% hydrogen by mass, can be produced from renewable hydrogen and nitrogen from the air. Its thermal properties are similar to propane, making it an attractive hydrogen and energy carrier. Ammonia has been used for over a century as a fertilizer, chemical raw material, and refrigerant. While it can be used as a fuel, challenges include low flammability, high NOx emissions, and low radiation intensity. Overcoming these challenges requires further research into ammonia flame dynamics and chemistry. The paper discusses recent applications of ammonia fuel in gas turbines, co-fired with coal, and in industrial furnaces, implemented under Japan's "Cross-ministerial Strategic Innovation Promotion Program (SIP): Energy Carriers." It also covers fundamental aspects of ammonia combustion, including characteristics of laminar premixed flames, counterflow twin-flames, and turbulent premixed flames stabilized by a nozzle burner at high pressure. The paper discusses the chemistry of ammonia combustion related to NOx production, processes for reducing NOx, and validation of ammonia oxidation kinetics models. LES results for a gas-turbine-like swirl-burner are presented to develop low-NOx single-fuelled ammonia gas turbine combustors. The paper also discusses the chemical kinetics of ammonia oxidation and fuel NOx, including the extended Zeldovich mechanism in ammonia combustion. Ammonia combustion is a promising alternative to fossil fuels for reducing greenhouse gas emissions, but challenges such as low flammability and high NOx emissions need to be addressed. The paper highlights the importance of ammonia as a carbon-free fuel and the need for further research into its combustion characteristics and chemistry.