This policy brief examines a central gap in the EU Emissions Trading System: while shipping companies now pay for their CO₂ emissions, there is no obligation to reinvest the resulting revenues in maritime decarbonisation. Drawing on France’s pioneering revenue-matching mechanism and mapping approaches across key European shipping nations, Camila Berreddad explores how Member States could better connect carbon revenues with investment in cleaner vessels, alternative fuels and port infrastructure. The brief calls for stronger EU-level incentives, greater traceability and independent environmental oversight to make carbon pricing a more effective tool for the maritime transition.