Universal exhibition

Universal Exhibition is the common name for the main events organized under the control of the International Bureau of Expositions. Though the great exhibitions held in the past were solely dedicated to showcasing industrial progress and showing off national prestige, nowadays they have become discussion platforms aimed at finding solutions to universal challenges of our time.

They are by definition international, meaning more than one Country takes part in them.

Alternative names for such events are World's Fair, World Expo, General Exposition or Registered Exhibition. The Historical exhibition are usually classified here within.

1988 Protocol
The 1988 BIE Protocol defines the bigger version of the Expos Registered Exhibitions. Their characteristics are: It doesn't specify if the participant countries have to build their pavilions at their expenses or not, but usually within Registered Exhibitions each country has its self-built pavilion, unless it participates into shared pavilions.
 * lasting minimum 3 weeks, maximum 6 months
 * they have to be organized every 5 years from 1995 (which means every year '0 and '5)

1972 Protocol
Universal Exhibition is the name given to the bigger expos in the Protocol of 1972 which defines them as follows:"An exhibition is universal when it displays the methods used and the progress achieved, or to be achieved, in several branches of human endeavour."

They could last minimum 3 weeks, maximum 6 months. The participating Countries had to build their pavilions at their own expense.

1928 Protocol
The original convention signed in 1928 defined the main international exhibitions as General Expositions; they were additionally divided into two sub-categories:  They included products of several branches of production or to be organized to bring out all the progresses made in a specific area (such as hygiene, applied arts, modern comfort, etc.). They could last minimum 3 weeks, maximum 6 months.
 * General Expositions of 1st Category, where participant countries had to build their own pavilions
 * General Expositions of 2nd Category, where participant countries didn't have the possibility to build their pavilions