The International Maritime Organization (IMO) is responsible for maintaining and updating the International Maritime Dangerous Goods Code (IMDG Code) which governs the vast majority of shipments of hazardous materials by water. The IMDG Code is intended to provide for the safe transportation of hazardous materials by vessel, protect crew members and to prevent marine pollution. The Code is based on the UN Model Regulations but also includes additional requirements applicable to the transport of hazardous materials by sea (e.g., requirements for marine pollutants, freight containers loading procedures, stowage and segregation and other requirements applicable to shipboard safety and preservation of the marine environment) that are not covered by the UN Model Regulations.

The IMDG Code is maintained and updated by IMO's DSC Sub-Committee. Implementation of the Code is mandatory in conjunction with the governments' obligations under the International Convention for the Safety of Life at Sea (SOLAS) and the International Convention for the Prevention of Pollution from Ships (MARPOL). The U.S. is signatory to these two conventions. Today at least 150 countries whose combined merchant fleets account for more than 98% of the world's gross tonnage use the IMDG Code as a basis for regulating sea transport of hazardous materials. The U.S. Hazardous Materials Regulations authorize use of the IMDG Code as a means of compliance with the HMR when at least one segment of transport involves sea transport.

The IMDG Code is currently up-dated every two years. The latest revision, Amendment 33, became effective on January 1, 2007. The IMO's Marine Safety Committee has recommended a twelve month transitional period through December 31, 2007 to allow users to become familiar with the new format. Amendment 33 is currently available from IMO as well as several commercial sources.

The IMDG Code has been recommended to Governments for adoption or for use as the basis for the national regulations to promote harmonization of regulations concerning the transport of dangerous goods by sea.