When a new pope needs to be chosen, he is voted on by the Catholic Church's most senior priests, called cardinals.
They travel from all over the world to the Vatican in Rome where the papal election - known as a conclave - is held.
The Vatican is home to the Catholic Church.
The voting is held in secret and a person needs more than two-thirds of votes to become the new Pope.
If that doesn't happen on the first vote, the cardinals will continue to vote until it does.
Smoke signals are used to tell people outside what is happening - black smoke means the cardinals are still making up their minds and will vote again.
When white smoke is released it means the new Pope has been chosen.