In Belgium, civil servants working for a European or international organization, and seconded national experts, have the right to ‘simplified residence’, which amounts to the issue of a ‘special identity card’ issued by the Foreign Affairs Ministry and not by the municipal authority. The members of their family can also take advantage of this system unless they are working in Belgium, because it is forbidden to work for a belgian employer with a special ID card! Holders of these special cards must not register in the commune where they live. They are however included in a separate local authority register and receive a national number (though this does not appear on their special identity card).
If you wish the special ID card
Consult the administrative procedure for the registration of staff members of International Organisations based in Belgium and their family members.