| IACS | - | International Association of Classification Societies |
| IAF | - | Inflation Adjustment Factor |
| IALA | - | International Association of Lighthouse Authorities |
| IAPH | - | International Association of Ports and Harbours |
| IAPP | - | International Air Pollution Prevention |
| IBC | - | International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk |
| IBIA | - | International Bunker Industry Association Ltd |
| IBS | - | Isthmus Bureau of Shipping |
| ICC | - | International Chamber of Commerce |
| | - | Institute Cargo Clauses |
| ICS | - | International Chamber of Shipping |
| ICS | - | Institute of Chartered Shipbrokers |
| IDL | - | International Date Line |
| IFF | - | Institute of Freight Forwarders |
| IFO | - | Intermediate Fuel Oil |
| IFP | - | Interim Fuel Participation factor |
| IGC | - | International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk |
| IGS | - | Inert Gas System |
| IHO | - | International Hydrographic Organisation |
| IHP | - | Indicated Horse Power |
| ILOHC | - | In Lieu Of Hold Cleaning |
| IMB | - | International Maritime Bureau |
| IMDG | - | International Maritime Dangerous Goods code |
| IMO | - | International Maritime Organisation |
| IMOSAR | - | IMO Search and Rescue manual |
| IMPA | - | International Marine Purchasing Association |
| INF | - | International Code for the Safe Carriage of Packaged Irradiated Nuclear Fuel, Plutonium and High-Level Radioactive Wastes on Board Ships |
| INMARSAT | - | International Maritime Satellite Organisation |
| INTERTANKO | - | International Association of Independent Tanker Owners |
| IOPP | - | International Oil Pollution Prevention |
| IOR | - | Indian Ocean Region |
| IP | - | Institute of Petroleum |
| IRO | - | In Respect Of |
| IRS | - | Indian Register of Shipping |
| ISDN | - | Integrated Services Digital Network |
| ISF | - | International Shipping Federation |
| ISGOTT | - | International Safety Guide for Oil Tankers and Terminals |
| ISM | - | International Safety Management code |
| ISMA | - | International Ship Managers Association |
| ISO | - | International Organisation for Standardisation |
| ISPP | - | International Sewage Pollution Prevention |
| ISPS | - | International Ship and Port Facility Security Code |
| ITF | - | International Transport Workers' Federation |
| ITIC | - | International Transport Intermediaries' Club |
| IU | - | If Used |
| IUHTAUTC | - | If Used, Half Time Actually To Count |
| IUMI | - | International Union of Marine Insurance |
| IWL | - | Institute Warranty Limits |
| IWO | - | In Way Of |
