Watch Leah's report...
Pope Francis's first day as head of the Catholic Church is underway.
He greeted people at one of Rome's main churches, Santa Maria Maggiore, before praying in private.
Later, he will lead cardinals in his first Mass and may start choosing the people he wants to work for him at the Vatican.
In the next few days he will visit Benedict, the last Pope, who resigned unexpectedly in February saying he was too old to keep going.
Pope Francis I was chosen as Benedict's successor by the most senior members of the Church after a series of secret votes.