Zero-emissions vessels are vessels that emits no greenhouse gasses or pollutants during its operation. Unlike fossil fuel powered ships, zero emission ships do this by utilizing propulsion systems which generate usable kinetic energy using alternative fuels. The ideal choice of technology is determined by vessel size, power requirements, and operational profile, and fuel availability.

These propulsion systems may include a combination of technologies such as fuel cells, batteries, or ICEs of hydrogen carriers that convert renewable energy into kinetic energy. As sailing distance and power requirements grow, the choice of onboard technology transition from battery-electric, to Hydrogen fuel cells (using gaseous or liquid hydrogen) and to more energy dense fuels such as ammonia or methanol for long-distance sailing (>1000 nautical miles). Fuels such as ammonia and methanol come with the caveat that they require after-treatment (ammonia) or onboard carbon capture (methanol) to ensure that no emissions are released into the atmosphere. Wind assisted propulsion technologies can also be integrated to reduce overall energy consumption on such vessels or extend the range of an alternative fuel propulsion system.

By entirely eliminating emissions from fossil fuel combustion, zero emissions ships contribute to mitigating climate change and reducing air and noise pollution in sensitive marine environments.