Classification societies are non-profit organisations that approve ship design, survey the construction of new vessels, issue certificates to and “class” vessels as seaworthy. They also perform periodic surveys of vessel for maintenance of class and certificates. Ship classification thus provides a benchmark on ship reliability and safety. Classification societies class the vessel and do the periodic surveys on behalf of the flag nation. National registers require that ships in their register be classed all the time. Marine insurers similarly require classification for the vessels they insure, as do the banks financing the vessels.
Several classification societies operate around the world. Classification rules for the major classification societies were standardised in 1968 when they established the International Association of Classification Societies (IACS) http://www.iacs.org.uk/ . IACS introduced uniformity in classification rules, interface between classification societies and collaboration between the societies and the International Maritime Organisation (IMO), the UN organisation that drafts and works to get conventions for international shipping and works for the implementation of these conventions. (IACS, 2012). See section 3.3.5 on conventions.
The thirteen IACS member classification societies cover more than 90 per cent of the cargo and passenger fleet. Lists of vessels classed by the IACS members are updated every week and may be downloaded from http://www.iacs.org.uk/shipdata/data.aspx?pageid=3§ionid=1