Before the ship is issued any certificate, the ship has to be registered in a certain country. This will issue the ship, the Flagstate of that country. Thus a Flagstate accepts a ship that carries its flag as belonging to its fleet. But this is not free. The Flagstate charges some amount or levy a tax to allow the ship to sail under its jurisdiction. Once done, the ship has to carry the name of the town where it's registered on the stern. The Flagstate also issues a International Tonnage Certificate which carries details of the ship such as dimensions, content of various spaces , gross tonnage etc. Producing this certificate involves a lot of calculation and measuring different areas of the ship.
Apart from that, Flagstate issues Minimum Safe Manning Certificate which states the minimum number of ship crew and staff required on a ship, and also the training required by them.A ship when on port is charged according to its tonnage. The tonnage certificate issued by Flagstate is used for this purpose. For e.g.- special tonnage certificates are issued by Suez and Panama canal on which their fees are based.
In the process of approving the ships, Classification Society and Flagstate work hand in hand. Classification society mainly looks after the technical issues of the ship while Flagstate ensures on board safety, personnel training, marine pollution prevention and ship to shore communication. But these functions are not "Domain Constrained". This means that Classification society and Flagstate often share the duties to look after the different processes. For e.g. Flagstates often delegate their tasks to Classification Society. Thus Classification Society can be seen issuing statutory certificates apart from class certificates.