Organisations
An organisation is any type of association which was present at EXPO 58, and which was not representing a country.
In general, many organisations were linked to partnerships between countries like Benelux or European Council.
I deliberately put Flanders and Walloon as an organisation, since strictly speaking they are not a country (and certainly not in 1958) but were more present as an organisation which represented a region/language.
For the rest, the same contents will be put as for the countries.
For your own convenience I have put the organisations in an alphabetic order. If there is something you can not find, check under countries or others.