Iranian authorities called for a snap presidential election, which according to the constitution must be held within 50 days of the declaration of the president's death or incapacity, and transferred Raisi's duties to First Vice President Mohammad Mokhber.
The four candidates on the ballot include reformist ex-health minister Masoud Pezeshkian and three conservatives: former nuclear negotiator Saeed Jalili, parliament speaker Mohammad Bagher Ghalibaf, and ex-interior minister Mostafa Pourmohammadi, listed in declining order of popularity according to opinion polls.
A second round of voting will take place on July 5, if necessary.
On May 19, Raisi died after his helicopter crashed on its way back to Iran from a visit to neighboring Azerbaijan. Preliminary findings of an official Iranian probe suggest the helicopter caught fire after hitting a hilltop amid thick fog.