World expos, known also as world's fairs in the United States, are recognized and sanctioned by the Bureau International des Exposition (BIE), an international body headquartered in Paris that came into existence in 1928.
There are now two "sizes" of world's fairs: a larger "sanctioned" 6-month expo and a smaller "recognized" 3-month expo. Expo 2020 will be the larger "sanctioned" category of world's fair.
Expo 2020 will follow Hannover, Germany's Expo 2000; Aichi, Japan's Expo 2005; Shanghai, China's Expo 2010; and Milan, Italy's Expo 2015. The bidding process for Expo 2020 has begun with five cities bidding: Ayutthaya (Thailand), Dubai (UAE), Izmir (Turkey), Sao Paulo (Brazil), and Yekaterinberg (Russia). A decision on 2020 will be made in 2013.
Bidding for Expo 2025 may start as early as 2016 with a decision in 2018. Once one city has bid, a 6-month window is created in which competing cities can bid for the same year.
See ExpoBids.com to check out the possible competition.