Crowds are gathered in St. Peter's Square in the Vatican for the formal installation of Pope Francis, who will preside over the world's 1.2 billion Roman Catholics.
The sky over Rome is a flawless blue as Pope Francis celebrates Mass with political leaders from 130 nations and representatives from a variety of religions. More than 30 delegations of other Christian churches, as well as representatives from the Jewish, Muslim and various other faiths, are attending.
Among the high-level guests, the spiritual leader of the world's Orthodox Christians, Bartholomew, was expected to attend. He would be the first patriarch from the Istanbul-based church to witness a papal inauguration since the two branches of Christianity split nearly 1,000 years ago.
Earlier Tuesday, Pope Francis took a turn around St. Peter's Square in an open-air vehicle to greet the faithful gathered there in his honor. Onlookers waved banners expressing support for the new leader of their church. The new pope paused several times to bless small children and, in one case, a man who appeared disabled.
Crowd size was expected to be in the hundreds of thousands.
Argentine President Cristina Fernandez de Kirchner arrived prior to Tuesday, in order to meet with the new pope, who hails from her country. U.S. Vice President Joe Biden, a Catholic, also is one of the political leaders in attendance.
In the pope's native Argentina, crowds gathered at the cathedral in the capital, Buenos Aires, in an overnight vigil to celebrate Francis's ascension to the papal throne.
The Vatican released Pope Francis' new coat of arms, which is similar to the one he used as Archbishop of Buenos Aires. It features symbols of Jesus, his mother Mary and her husband Joseph, as well as the new papal trappings of a bishop miter and the crossed keys of the Holy See.
Pope Francis last week was elected to replace Pope Benedict, who stepped down, citing his age and health.
Vatican officials also released details of Francis' official ring, which once was offered to Pope Paul VI, who presided over the second half of the Second Vatican Council, which is credited with modernizing the Roman Catholic Church.
Francis receives the ring during Tuesday's installation Mass.