The 133 cardinal electors due to choose a successor to late Pope Francis gathered inside the Vatican's chapel on Wednesday to begin the secretive century's old ritual known as the conclave.
The cardinal electors will be locked inside the chapel where they will hold as many rounds of voting as necessary to select the 267th leader of the world's 1.4 billion Catholics.
The process can take several days.
After a cardinal receives the required number of votes and agrees to become the new pontiff, white smoke will signal his selection.