Due to climate change the International Maritime Organization (ΙΜΟ) has set limits to the shipping sector in order for emissions to be mitigated. The marine industry will see a quick energy and technology shift that would have a greater influence on asset values, earning capacity and costs than previous transitions. Shipowners are already under increasing pressure to minimize marine transportation’s greenhouse gas footprint. The use of an alternative fuel seems to be a strong solution so as to achieve the sustainable targets of the Paris Agreement. This thesis evaluates the potential of ammonia as a marine fuel, a promising energy carrier and carbon free combustible fuel, in comparison with other alternative fuels like Hydrogen, Methane, LNG, LPG, Bio-Fuels and Batteries. It also uses multi-criteria decision analysis (MCDA) to solve serious shipowners concerns. In addition, it takes into account all the aspects of ammonia as a hydrogen carrier, as well as the relevant legislation and rules, port infrastructure, cost and environmental efficiencies, technological maturity and scalability. The findings of this thesis suggest that various alternative fuels have potential, but more research is needed before definite conclusions can be drawn about ammonia’s potential as an alternative marine fuel.