International Association of Classification Societies (IACS) is a technically based non-governmental organization which today consists of eleven members of marine classification societies.
More than 90% of the world's cargo-carrying ship tonnage is covered by the classification standards set by the member societies of IACS.
According to IACS, the members must, among other things, recognize certificates across the membership. More details can be found in - Classification societies – what, why and how? which may be downloaded here.