The Convention of the Metre is an intergovernmental treaty open to all States having diplomatic relations with France (the depository of the Treaty) and willing to pay their annual contribution to the BIPM.
The procedure for a State to join is as follows:
Preliminary contact is made with the Director of the BIPM.
The government of the State wishing to join the Convention of the Metre informs the French Foreign Minister of its intent by letter delivered through its embassy in Paris.
At the same time, payment of the first annual contribution plus an entry fee equal to the first annual contribution is made directly to the BIPM.