Classification societies are organizations that establish and apply technical standards in relation to the design, construction and survey of marine related facilities including ships and offshore structures. These standards are issued by the classification society as published rules. A vessel that has been designed and built to the appropriate rules of a society may apply for a Certificate of Classification from that society. The society issues this certificate upon completion of relevant classification surveys.

Such a certificate does not imply, and should not be construed as an express warranty of safety, fitness for purpose or seaworthiness of the ship. It is an attestation only that the vessel is in compliance with the standards that have been developed and published by the society issuing the classification certificate.

Classification rules are developed to contribute to the structural strength and integrity of essential parts of the ship’s hull and its appendages, and the reliability and the function of the propulsion and steering systems, power generation and those other features and auxiliary systems which have been built into the ship in order to maintain essential services on board.

A ship is maintained in class provided that the relevant rules have, in the opinion of the society concerned, been complied with and surveys carried out in accordance with its rules.

The most common classification bureaus are:
LR Lloyd's Register
DNV Det Norske Veritas
ABS American Bureau of Shipping
GL Germanischer Lloyd
BV Bureau Veritas
RINA Registro Italiano Navale