Before the creation of the Bureau International des Expositions (BIE), no official, international standard was successfully implemented to categorize World Expos. The Convention Relating to International Exhibitions (1928) established an internationally agreed official categorization system that entered into force in 1931, and has been modified twice. We call these four categorization frameworks Pre-BIE, First, Second, and Third Systems.

​

* We are currently in the progress of updating the individual pages for each Expo so some links may not work.