The papal conclave begins May 7. Here's how cardinals choose the next pope, what to expect and how secretive the process is.

For centuries, the head of the Roman Catholic Church has been chosen through what’s known as a papal conclave. The proceedings are cloaked in secrecy, making them the subject of speculation and intrigue.

One hundred and thirty-three cardinals are sequestering themselves behind the Vatican’s medieval walls for the start of a conclave to elect a successor to Pope Francis.