As a specialized agency of the United Nations (UN), the International Maritime Organization (IMO) plays a key role in regulating maritime activities on the high seas which are beyond the sovereignty and jurisdiction of any particular state. The IMO’s Marine Environment Protection Committee (MEPC) adopted the international convention for the prevention of MARine POLlution from ships (MARPOL) in 1978, and revised it in 2011 to include regulations to reduce CO2 emissions reduction from international shipping in response to global climate concerns. To assess the carbon intensity of ships, the IMO introduced the energy efficiency design index (EEDI) for newbuild ships, the energy efficiency existing index (EEXI) for existing ships, and the carbon intensity indicator (CII), which assesses the annual operational performance of international shipping. The IMO has strengthened greenhouse gas reduction targets, aiming for net-zero emissions by 2050. Future regulations are expected to consider the well-to-wake (WtW) GHG emissions intensity based on lifecycle assessments, including greenhouse gases other than CO2.