This document is a guide that discusses the significance of renewable and low-carbon ammonia in the decarbonization of the maritime transport sector. It outlines the current challenges and opportunities associated with the adoption of ammonia as a sustainable shipping fuel. The guide details how ammonia can be produced through renewable hydrogen or low-carbon hydrogen methods, emphasizing its potential to reduce greenhouse gas emissions in shipping. It also highlights the role of regulatory frameworks, such as the FuelEU Maritime initiative, in promoting the use of alternative fuels. The document presents recommendations for fostering a market for renewable and low-carbon ammonia, including tax incentives for shipping companies, collaboration with international organizations for regulatory harmonization, and investment in bunkering infrastructure. The guide stresses the importance of early investments in the shipping value chain to facilitate the transition to zero-carbon fuels and ensure the competitiveness of ammonia in the maritime sector.