This paper explores the potential of ammonia as a carbon-free fuel and discusses recent advancements in ammonia combustion technology and its underlying chemistry. The Paris Agreement aims to limit global temperature rise to below 2°C, requiring the de-carbonization of energy generation through the use of carbon-neutral and carbon-free fuels. Hydrogen is a promising energy carrier, but its long-distance shipment and storage pose challenges. Ammonia, which contains 17.8% hydrogen by mass, can be produced from renewable hydrogen and nitrogen from the air, making it an attractive alternative. Ammonia has been used for fertilizer, chemicals, and refrigeration for over a century and can also serve as a fuel. However, challenges such as low flammability, high NOx emissions, and low radiation intensity need to be addressed. The paper reviews successful applications of ammonia fuel in gas turbines, co-fired with pulverized coal, and industrial furnaces, as part of Japan's "Cross-ministerial Strategic Innovation Promotion Program (SIP): Energy Carriers." It also delves into the fundamental aspects of ammonia combustion, including flame dynamics, chemistry, and NOx reduction processes. The paper presents LES results for a gas-turbine-like swirl-burner to develop low-NOx single-fuel ammonia gas turbine combustors.This paper explores the potential of ammonia as a carbon-free fuel and discusses recent advancements in ammonia combustion technology and its underlying chemistry. The Paris Agreement aims to limit global temperature rise to below 2°C, requiring the de-carbonization of energy generation through the use of carbon-neutral and carbon-free fuels. Hydrogen is a promising energy carrier, but its long-distance shipment and storage pose challenges. Ammonia, which contains 17.8% hydrogen by mass, can be produced from renewable hydrogen and nitrogen from the air, making it an attractive alternative. Ammonia has been used for fertilizer, chemicals, and refrigeration for over a century and can also serve as a fuel. However, challenges such as low flammability, high NOx emissions, and low radiation intensity need to be addressed. The paper reviews successful applications of ammonia fuel in gas turbines, co-fired with pulverized coal, and industrial furnaces, as part of Japan's "Cross-ministerial Strategic Innovation Promotion Program (SIP): Energy Carriers." It also delves into the fundamental aspects of ammonia combustion, including flame dynamics, chemistry, and NOx reduction processes. The paper presents LES results for a gas-turbine-like swirl-burner to develop low-NOx single-fuel ammonia gas turbine combustors.