The Vatican is set to elect its 266th pope, as 115 Roman Catholic cardinals begin their closed-door papal election on Tuesday.
The cardinals attended mass at St. Peters basilica and moved into the Vatican with no clear frontrunner set to lead the world's 1.2 billion Catholics.
Cardinal Angelo Sodano gave the homily and called for cooperation and unity, according to CNN.
"My brothers, let us pray that the Lord will grant us a pontiff who will embrace this noble mission with a generous heart," Sodano told the congregation.
The conclave will take place in the Sistine Chapel and the cardinals will live inside the Vatican - cut off from the world - until they elect a new pope.
As Reuters points out, "No conclave has lasted than more than five days in the past century. Pope Benedict was elected within barely 24 hours in 2005 after just four rounds of voting."
The cardinals - who must be younger than 80 to vote - are divided into two parties, the Roman Party, known as the Curia, and the so-called reformers.
It's not really a liberal and conservative divide inside the Vatican. The schism is between those who want to maintain the status quo and reformers, according to the BBC.
The cardinals may not communicate with journalists or anyone from the outside world, and that includes sending tweets. If a cardinal breaks this rule he could be excommunicated, according to Deutsche Welle.
The Vatican will use smoke signals to tell the world if a new pope has been elected. Black smoke means the no pope has been elected, and white smoke means the cardinals have reached a two-thirds majority (77 votes) and Catholics have their new spiritual leader.
There will be four votes per day, two in the morning and two in the afternoon, except on Tuesday. The cardinals do not have to vote today, but a Vatican spokesman said they probably would, according to CNN.