Tokyo is making its second successive bid to host the Games, having lost the vote for 2016 to Rio de Janeiro, and is seeking to host its second Olympiad following the 1964 Tokyo Olympic Games.
Istanbul is making its fifth bid to host the Olympics in succession, Madrid is applying for the third time in a row, while Baku, Azerbaijan, and Doha, Qatar, have also saddled up again after falling in the race to hold the 2016 Games.
The number of cities bidding to host the Games is one fewer than the seven that sought to hold the 2016 Olympiad.
Bidding cities must file applications including an overview plan for hosting to the International Olympic Committee (IOC) by Feb. 15 next year. Two cities will be eliminated from the race in May next year after preliminary qualifying. The IOC will decide on the host city during an IOC Session in Buenos Aries on Sept. 7, 2013.