International Bureau of Exhibitions made stipulations after establishing in 1928, must confirm a theme in every World Expo, and has implemented since World Expo of Chicago of U.S.A. of 1933.

• 1928年国际展览局成立后作出规定，每一届世博会必须要确定一个主题，并从1933年美国芝加哥世博会开始实施。