The Metre Convention is an intergovernmental treaty which is open to all states having diplomatic relations with France (the depository of the Treaty) and willing to pay their entrance fee and annual contribution to the BIPM.
Overview of the procedure for a state wishing to accede to the Metre Convention and thus become a Member State of the BIPM:
After being motivated to participate in the activities of the BIPM contact should be made with the Director of International Liaison and Communication Department (Mr Andy Henson) or the BIPM Director (Dr Martin Milton) who can provide detailed advice on the rights and obligations and on the accession process.
Having decided to proceed, a state must make the formal national decision to accede in accordance with its own constitutional requirements.
The Government of the State must then notify the French Government (i.e. Ministry for Europe and Foreign Affairs) through its ministry in charge of foreign affairs/Embassy in Paris* of its accession to the Metre Convention, including deposition of the national instrument of accession (decision document).
The payment of the first annual contribution (per calendar year) plus an entrance fee**
equal to the first annual contribution must be made directly to the BIPM.
* Not all states have an Embassy in Paris, and such states make arrangements to deal with the French Ministry for Europe and Foreign Affairs through, for example, their Embassy in Belgium
** Special arrangements apply regarding the entrance fee of states that were Associate States of the CGPM at the time of accession