Pope Francis's death at the age of 88 means the Catholic Church must choose a new leader. Here's how cardinals elect the next pontiff at the conclave.

Red-hatted cardinals were expected to pick a date Monday for the conclave to elect a new leader of the world's 1.4 billion Catholics, following the death of Pope Francis.Dozens of so-called "Princes of the Church" from across the world have been gathering at the Vatican since the 88-year-old Argentine pontiff died on April 21.