This dissertation, titled The Adoption of Alternative Fuels in the Maritime Sector, critically examines the decision-making processes in the maritime industry under the lens of Institutional Theory and the Multi-Level Perspective (MLP) on sustainability transitions. Employing a mixed-method approach, which integrates a comprehensive literature review with a detailed survey, the study explores how institutional pressures and sustainability transitions influence the shift toward low-carbon fuels in maritime operations. The research identifies key enablers such as technological innovations and economic incentives, and addresses barriers including high initial costs, infrastructural limitations, and regulatory challenges. It also highlights the significant influence of coercive, normative, and mimetic pressures in shaping organizational behaviours towards sustainable practices. A novel decision-making framework that synthesizes insights from Institutional Theory and MLP is proposed to facilitate the adoption of alternative fuels, supporting maritime companies in navigating the complexities of sustainability transitions. A research agenda is also put forward. The practical relevance of this study lies in its strategic framework, which provides actionable insights for maritime companies pursuing environmental sustainability. Academically, the dissertation makes a significant theoretical contribution by applying and extending Institutional Theory and MLP within the context of maritime fuel transitions, enhancing our understanding of the interplay between institutional dynamics and sustainability practices in the maritime industry.