In April 2018, the International Maritime Organization agreed on its initial strategy on GHG emissions from ships, to cut carbon emissions from shipping in half by 2050 relative to 2008 levels. At the same time, maritime transport will remain the backbone of world trade and global supply chains, growing by around 2.5 times by 2050, at almost 3% per year. With no clear strategy to achieve the ambitious decarbonization targets, the outlook is uncertain. What pathways can be adopted to ensure GHG emissions targets can be met, and what are the advantages and disadvantages? How will new propulsion technologies change the outlook in terms of substitution and fuel efficiency—and how fast can they be implemented? What options are available to the shipping and energy industries—from novel zero-carbon fuels to other technological improvements—to improve efficiency or capture carbon?