The decarbonisation of shipping is a key step in the global fight against climate change. The International Maritime Organisation (IMO) has adopted mandatory measures to reduce emissions of greenhouse gases from international shipping. One proposal is ammonia – a potential marine fuel. One drawback, however, is the risk of nitrous oxide (N2O) emission. The EU-funded ENGIMMONIA project will promote the global introduction of alternative fuels like ammonia and transfer clean energy technologies successfully demonstrated in terrestrial applications like waste heat recovery and renewables to the maritime sector. It will explore the benefits of carbon-free fuel for vessel engine application and develop an exhaust aftertreatment system.