The Organisation consists of an Assembly, a Council and five main Committees: the Maritime Safety Committee; Marine Environment Protection Committee; Legal Committee, Technical Co-operation Committee; and a Facilitation Committee.
This is the Governing Body of the Organisation. It consists of all Member States, and it meets once every two years in regular sessions; but may also meet in extraordinary session if necessary. The Assembly is responsible for approving the work programme, voting the budget and determining the financial arrangements of the Organisation. The Assembly also elects the Council.
The Council is composed of 32 Member States elected by the Assembly for two-year terms beginning after each regular session of the Assembly. The IMO Convention provides that in electing the Members of the Council the Assembly shall observe the following criteria: (a) Eight shall be States with the largest interest in providing international shipping services; (b) Eight shall be other States with the largest interest in international seaborne trade; (c) Sixteen shall be States not elected under (a) or (b) above which have special interests in maritime transport or navigation, and whose election to the Council will ensure the representation of all major geographic areas of the world.
In November 1993 the Assembly adopted an amendment to the IMO Convention which, upon entry into force, will increase the size of the Council to 40. Groups (a) and (b) will be increased to 10 Members and Group (c) to 20. The amendment will enter into force 12 months after being accepted by two-thirds of IMO Member States.
The Council is the Executive Organ of IMO and is responsible, under the Assembly, for supervising the work of the Organisation. Between sessions of the Assembly the Council performs all the functions of the Assembly, except the function of making recommendations to Governments on maritime safety and pollution prevention which is reserved for the Assembly by Article 15(j) of the Convention. Other functions of the Council are to:
The Members of the Council elected by the 21st Assembly in 1999 for 2000-2001 are as follows:
The MSC is the highest technical body of the Organisation. It consists of all Member States. The functions of the Maritime Safety Committee are to "consider any matter within the scope of the Organisation concerned with aids to navigation, construction and equipment of vessels, manning from a safety standpoint, rules for the prevention of collisions, handling of dangerous cargoes, maritime safety procedures and requirements, hydrographic information, log-books and navigational records, marine casualty investigation, salvage and rescue, and any other matters directly affecting maritime safety".
The Committee is also required to provide machinery for performing any duties assigned to it by the IMO Convention or any duty within its scope of work which may be assigned to it by or under any international instrument and accepted by the Organisation. It also has the responsibility for considering and submitting recommendations and guidelines on safety for possible adoption by the Assembly.
The MSC operates with the assistance of nine Sub-Committees. These are:
The Legal Committee is empowered to deal with any legal matters within the scope of the Organisation. The Committee consists of all Member States of IMO. It was established in 1967 as a subsidiary body to deal with legal questions which arose in the aftermath of the Torrey Canyon disaster. The Legal Committee is also empowered to perform any duties within its scope which may be assigned by or under any other international instrument and accepted by the Organisation.
The MEPC, which consists of all Member States, is empowered to consider any matter within the scope of the Organisation concerned with prevention and control of pollution from ships. In particular it is concerned with the adoption and amendment of conventions and other regulations and measures to ensure their enforcement. The subcommittees on Bulk Liquids and Gases and Flag State Implementation are also subsidiary bodies of the MEPC as far as pollution aspects are concerned. The MEPC was first established as a subsidiary body of the Assembly and raised to full constitutional status in 1985.
The Technical Co-operation Committee is required to consider any matter within the scope of the Organisation concerned with the implementation of technical co-operation projects for which the Organisation acts as the executing or co-operating agency and any other matters related to the Organisation's activities in the technical co-operation field. The Technical Co-operation Committee consists of all Member States of IMO, was established in 1969 as a subsidiary body of the Council, and was institutionalised by means of an amendment to the Convention which entered into force in 1984.
The Facilitation Committee is a subsidiary body of the Council. It was established in May 1972 and deals with IMO's work in eliminating unnecessary formalities and "red tape" in international shipping.
The Secretariat of IMO consists of the Secretary-General and nearly 300 personnel based at the headquarters of the Organisation. The secretary-general of the Organisation is Mr. W.A. O'Neil of Canada who was appointed to the position with effect from 1 January 1990.
The holders of the office have been:
The approved regular budget appropriations for 2000-2001 totalled £36,612,200, the same as for 1997-1998. Contributions to the IMO budget are based on a formula which is different from that used in other United Nations agencies. The amount paid by each Member State depends primarily on the tonnage of its merchant fleet. The top ten contributors for 1999 were assessed as follows (the figures show the amount payable and as a percentage of the total budget):
| serial no. | country | £m | % |
| 1 | Panama | 2.90 | 15.80 |
| 2 | Liberia | 1.86 | 10.17 |
| 3 | Japan | 0.96 | 5.23 |
| 4 | Bahamas | 0.81 | 4.36 |
| 5 | Greece | 0.80 | 4.32 |
| 6 | USA | 0.76 | 4.12 |
| 7 | Malta | 0.73 | 3.96 |
| 8 | Cyprus | 0.72 | 3.91 |
| 9 | Norway | 0.71 | 3.86 |
| 10 | Singapore | 0.61 | 3.31 |